The Russian embassy in Damascus was mortared Tuesday while the Russian military buildup in Syria continued with as many as 28 Russian attack jets now reportedly at an airfield near the northwestern town of Latakia.
Two mortar shells landed on the embassy ground but there were no reports of casualties or major damage.
"One of them fell near the main entrance, the other hit an administrative building," Asiya Turuchiyeva, the embassy's spokeswoman, told the Russian outlet RIA Novosti.
The shells were fired from a Damascus area controlled by "illegal armed groups," the Russian Foreign Ministry said.
"We treat the incident as terrorist act, aimed against the Russian Embassy," said Aleksandr Lukashevich, a Foreign Ministry spokesman. "We reaffirm our solidarity with the Syrian authorities in their efforts to combat the terrorist threat in the territory of Syria."
The Russian embassy also came under fire last May in an attack that also caused no casualties.
The latest attack was seen as a possible opening salvo by the Syrian opposition to the Russian military buildup in recent weeks in support of the regime of Syrian President Bashar al-Assad.
In addition to military advisers and equipment, Russia has now sent 28 attack jets along with attack helicopters and cargo planes to the airfield near Latakia, Agence France-Presse reported.
The Russian advisers have also begun flying surveillance drone flights out of the airfield, Reuters reported.
At the Pentagon, spokesman Navy Capt. Jeff Davis said he could not confirm the specifics of the buildup but did not discourage reporters from citing the numbers.
"We're obviously watching, we're keenly aware of what is happening there," Davis said. "We continue to believe that anything that's done in support of the Assad regime, particularly militarily, is counterproductive and risks worsening an already bad situation."
Secretary of State John Kerry over the weekend confirmed that Russian warplanes were on the ground in Syria but Davis said he could not as yet give the Pentagon's confirmation.
"I'm just going to tell you we're watching it closely," Davis said. ‘I'm not at liberty to disclose the intelligence we have."
Last Friday, Defense Secretary Ashton Carter spoke for the first time since taking office in February with his Russian counterpart, Sergei Shoygu.
Davis said the discussions focused mainly on "de-confliction," or avoiding confrontations between Russian and U.S. and coalition aircraft that could soon be operating at cross-purposes in the same airspace over Syria, with the Russians backing Assad while the U.S. focused on hitting militants affiliated with the Islamic State in Iraq and Syria.
At the State Department, chief spokesman John Kirby said, "If there's a constructive role they (the Russians) want to play against ISIL, we're willing to have that conversation." He was referring to another name for ISIS. However, if the Russian intent is to "prop up Assad, that's a whole different matter," Kirby said.
--Richard Sisk can be reached at Richard.Sisk@military.com.