Moscow said it would take immediate steps to clarify what had happened, and reiterated its longstanding insistence on a political solution and “the unacceptability of any kind of external intervention.”

The Russian foreign ministry did not comment specifically on the accusations that the target was a convoy carrying antiaircraft weapons. Speaking about the airstrikes, Aleksandr K. Lukashevich, a foreign ministry spokesman, said at a briefing later on Thursday:

“We are analyzing all the information that is available, and if it is confirmed then our main conclusion is that it is a very serious violation of the U.N. charter, an unacceptable act against a sovereign nation. But again, on the details, we are gathering information in order to present a fuller picture.”

When asked again about whether the target was a convoy, he said: “Our statement refers to the attack of Israeli air force on a Syrian facility near Damascus, we are checking this information. There are many assertions around in the international press. I have seen this statement, but we have no information about this from our American partners. I know for sure that Israeli side warned Washington, and there was a public announcement by the vice prime minister also made it clear that they would take military action if necessary.”

In Beirut, the Hezbollah also condemned the attack and offered support. “Hezbollah expresses its full solidarity with Syria’s leadership, army and people,” it said in a statement. Lebanon’s minister of foreign affairs, Adnan Mansour, said the Israelis attacked a research center, calling it “flagrant aggression.”

Iran, which has firmly allied itself with Mr. Assad, sending personnel from its Islamic Revolutionary Guards Corps. to Syria and ferrying military equipment to Syria through Iraqi airspace, said in a statement through its foreign minister, Ali Akbar Salehi:

“There is no doubt that this was an overt assault based on the West’s policy, and the Zionists got ahead of themselves in trying to cover up the successes of the Syrian government and nation in maintaining the existing government and restoring stability and security,” the Iranian Students’ News Agency quoted Mr. Salehi as saying.

Image Denying reports, Syria said Israeli jets had hit a defense research facility in Jimraya. Credit... The New York Times

“The attack reveals and proves the rightfulness of the government and nation of Syria in supporting Hamas and their enmity with Zionists, and it also shows that the terrorist groups are aligned with Zionists’ goal in undermining stability and calmness in the country,” Mr. Salehi said.