BEIRUT, Lebanon — In a second day of raids in Syria, Russian warplanes carried out a new round of airstrikes on Thursday that once again — contrary to Moscow’s assertions — appeared to be targeting not the Islamic State but a rival insurgent coalition.
Russia sent more than 50 aircraft on about 30 sorties over Syria on Thursday, using drones and satellites to identify targets, said Maj. Gen. Igor Konashenkov, a Defense Ministry spokesman. They were able to deploy quickly, he said, because ammunition and other supplies had been stockpiled at the Tartus naval base on Syria’s Mediterranean coast, Russia’s only military site outside the former Soviet Union.
Russia’s entry into the Syrian conflict, which started on Wednesday with a bombing attack on Syrian opposition fighters, has been angrily condemned by United States officials. They fear that President Vladimir V. Putin of Russia is using their shared goal of defeating the Islamic State as a pretext for weakening other opponents of Syria’s embattled president, Bashar al-Assad. Mr. Putin says that Mr. Assad is a bulwark against the Islamic State, also known as ISIS or ISIL; President Obama says that Mr. Assad must go, though perhaps in a “managed transition” to a new government.
The new round of strikes on Thursday — conducted with two models of Soviet-era warplanes, the Su-25 Frogfoot and Su-24 Fencer — was said by Mayadeen, a pro-Damascus news channel, to target the Army of Conquest, a coalition of insurgent groups that includes the Al Qaeda-affiliated Nusra Front, the hard-line Islamist group Ahrar al-Sham and a range of less extreme Islamist groups — all of which are opposed to the Islamic State.
Russian officials nonetheless insisted that they had hit four “objects of the Islamic State” in the provinces of Idlib, Hama and Homs. The Islamic State is most active in areas significantly to the east of those regions. Russia, like Mr. Assad, has tended to make little distinction among the many insurgent groups in Syria’s four-year-old civil war.
And the Russian military incursion may not be limited to Syria, the deputy foreign minister, Ilya Rogachev, suggested on Thursday in Moscow. He indicated that Moscow would be receptive to an invitation by Baghdad to assist in the fight against Islamic State in that country.
Later, in a news conference at the United Nations, the Russian foreign minister, Sergey V. Lavrov, said there no immediate plans to hit targets in Iraq. “We were not invited. We were not asked. We are polite people.”
In response to a question about which organizations in the region Russia considers to be fair targets, Mr. Lavrov was equally vague, saying: “If it looks like a terrorist, walks like a terrorist, acts like a terrorist, fights like a terrorist, it’s a terrorist, right?”
The Russian airstrikes, a major new twist in the war, come after a series of setbacks that had put Mr. Assad in his shakiest position in years.
A government soldier serving in Homs province said the Russian military support had arrived just in time. “Without the Russians,” he said, Islamic State forces could have reached the provincial capital of Homs, “and I don’t just think so, I’m sure.
“It should have started a long time ago,” he added, speaking by phone and asking not to be identified for fear of repercussions for speaking to a foreign news outlet. “Now, half the people have died or emigrated.”
Government forces lost ground in recent months not only to the Islamic State in the east and center of the country, but also to the Army of Conquest in the northwest, where its advances have posed the war’s sharpest threat to the coastal provinces that are Mr. Assad’s base.
By striking at the group, Russia is unlikely to be able to give Mr. Assad full control over the country, but could help him buy time, extending the deadly standoff — and prompting United States allies, like Saudi Arabia and Turkey, to pour more matériel into the conflict.
Often fighting alongside the Army of Conquest are relatively secular groups from what is left of the loose-knit Free Syrian Army, including some that have received United States training and advanced American-made antitank missiles. At least one C.I.A.-trained group was among the targets hit on Wednesday, which drew an angry response from Washington.
This year, the Army of Conquest dealt Syrian forces a serious setback by seizing the city of Idlib, and later the entire province, advances that posed the war’s sharpest threat to the coastal areas where support for Mr. Assad is strongest. Russia has a naval station on the coast and has concentrated much of its recent military buildup there, so Thursday’s strike could be seen as a force-protection measure, taking out the insurgents closest to Russian installations before moving on to other operations.
There have also been reports from insurgents on the ground that extremist groups of Russian-speaking fighters have moved into the mountains straddling Idlib and Latakia, including Jaish al-Muhajireen Wal Ansar, or the Army of Emigrants and Supporters, which includes many Chechens. Russia has fought two wars with its semiautonomous republic Chechnya, and many Chechens and other Russian Muslims from the Caucasus Mountains and Central Asia have joined the Islamic State or other groups in Syria. Russia’s concern about the more than 2,000 Russian citizens who have fought in Syria — and who might later carry out attacks back home — is another reason for its intervention.
But the choice of target underlined a fundamental dispute between the United States, its allies, and Syrian opponents of Mr. Assad on one hand, and Mr. Assad and Russia on the other.
The Russian state news agency RIA reported on Thursday that airstrikes by the Syrian military, which is working with the Russian Air Force, had killed 107 militants, including three commanders of the Nusra Front, Al Qaeda’s affiliate in Syria, near Homs.
But Konstantin Kosachev, the chairman of the foreign affairs committee of the Russian Senate, denied the charge that Russia was overlooking Islamic State targets and instead attacking other opponents of Mr. Assad’s. “There is no evidence able to prove these groundless claims that are being spread today,” he said.
Mr. Assad, and now Russia, make little distinction among Islamist insurgent groups, and their supporters suggest that any such distinctions are meaningless hairsplitting. United States policy appears to reflect an acknowledgment that the Nusra Front and its allies — while many of them are unpalatable — often clash with the Islamic State and have differing goals and tactics.
Syria’s ambassador to Russia, Riad Haddad, held a news conference on Thursday in which he gave full-throttled support to everything the Russian military was doing.
The attacks were all carried out in coordination with the Syrian military, he said, adding that it did not matter who was being attacked because all of the groups fighting the government were “terrorists” who subscribed to the same goals as the Islamic State.
“We in Syria encounter various armed terrorist groups, and regardless of what they are called,” Mr. Haddad said, citing the Nusra Front, the Islamic State and the Free Syrian Army as examples, “they all pursue the same terrorist goals.”
He referred to the airstrikes near the cities of Homs and Hama as the fruit of Syrian information combined with Russian firepower.
“There are precise position data for the places where the terrorist groups are,” Mr. Haddad said. “This is why the airstrikes are carried out only against the positions of the Islamic State in some cities or outskirts, like, for example, of Homs and Hama.”
Mr. Haddad said the Russian attacks would likely be more effective than what he called the illegal strikes carried out by American and other Western forces in the past year.
“We have not seen any results on the ground,” the ambassador said. “Actually, just the opposite: The Islamic State expanded.”
He added, “We can say that we have begun to hit the terrorists in an organized manner.”
The Syrian uprising began in 2011 with peaceful protests and turned violent in response to repression by the government. But relatively secular groups led by army defectors have been eclipsed by better-financed, better-organized Islamist groups.
In the United States, Secretary of State John Kerry and Defense Secretary Ashton B. Carter have denounced Russia’s first round of airstrikes, pointing out that even as Russian pilots did not hit known strongholds of the group. Instead, they targeted areas held by other insurgents, including some American-trained ones, in strikes that killed 40 people, including some civilians.
But the Army of Conquest itself embodies the ambivalence of American policy. The United States considers the Nusra Front a terrorist organization, but other groups, including some that have received American funding, fight alongside Nusra, saying that they have no choice if they want to unseat Mr. Assad.
The United States has been reluctant to increase support to those groups because some weapons have ended up in the hands of the Nusra Front, and Washington does not want to see the militant group take over Syria any more than it wants the Islamic State to take power.
Because of an editing error, an earlier version of this article referred incorrectly to Sergey V. Lavrov. He is the Russian foreign minister, not, of course, the Soviet one (since the Soviet Union ceased to exist long ago).