Damascus, Syria (CNN) Syria and its most powerful ally, Russia, blamed Israel for striking an air base in the war-torn country on Monday, following a suspected chemical gas attack that drew condemnation from world powers.

Russia's Defense Ministry claimed two Israeli F-15 warplanes launched eight guided missiles from Lebanese territory, targeting the T-4 base in central Syria. The Defense Ministry said Syrian defense units destroyed five of the incoming missiles.

The Lebanese Army issued a statement alleging a number of violations of Lebanese airspace by Israeli aircraft between Sunday and Monday. The statement stopped short of accusing Israel of being behind the attack on the T-4 base.

Syrian state media said that a number of people were killed or injured in the strikes and cited a military source blaming Israel for the military action.

Israeli officials have not issued any response to reports of the strike, but its warplanes hit the same facility in February, after Israel said an Iranian drone had infiltrated its airspace. Israeli officials said Iran, a key backer of the Syrian government, was using the T-4 facility as a command center.

Key developments:

At least four Iranian military advisers were killed in the strike, Iranian state media reported.

Russia complained Israel did not inform it of any planned strike, despite a deconfliction agreement.

The strike comes two days after activists said a suspected chemical attack in Douma killed dozens.

US President Donald Trump vowed a response in the next two days to the "atrocious" suspected chemical strike.

Russian Foreign Minister Sergey Lavrov claimed there was "no trace" of chemical weapons use there.

Israel active in Syria

The Syrian conflict has developed into a complex proxy war, which in recent years has included Israeli strikes on Iran-linked targets.

Israel's official stance on the war is neutral, but it has acknowledged carrying out some strikes on Syrian military targets, while denying responsibility for numerous others. It has clearly stated in the past that it would respond to Iran's growing presence in Syria.

Defense Minister Avigdor Lieberman said in a March interview with the Yedioth Ahronoth newspaper that Israel had been acting militarily in Syria in recent months. "A large part of Israeli army activity does not find its way on to (Israeli newspapers and websites) ... and that is good," he said. "It's just not right to say that we don't act."

over Syria for deconfliction since Russian forces entered the country in late 2015. The T-4 base, located in a Israel and Russia have typically coordinated their military actionsover Syria for deconfliction since Russian forces entered the country in late 2015. The T-4 base, located in a strategic position between the cities of Homs and Palmyra in Syria's west, has been a key staging ground for Syrian and Russian aircraft during the war.

But Dmitry Peskov, a spokesman for Russian President Vladimir Putin, said there had been no contact between Israel and Russia before or during Monday's airstrike, adding the lack of communication was a "cause for concern."

Peskov said Putin intended to speak with Israeli Prime Minister Benjamin Netanyahu on the issue as Russian advisers were still at the T-4 base.

Syria had earlier speculated that the United States was behind Monday's strikes, which the Pentagon swiftly denied.

Trump: 'Big price to pay' in Syria

Syrian activist groups said toxic gas inside barrel bombs were dropped from helicopters over the rebel-held city of Douma on Saturday, killing dozens of civilians and wounded scores more.

Graphic footage shot by rescuers and activists show victims -- including children -- dead and injured, some ghostly white and foaming at the mouth in makeshift clinics. Others were found suffocated in their homes, according to first responders.

CNN could not independently verify the authenticity of the images.

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The Syrian government and Russia vehemently denied involvement and accused rebels in Douma of fabricating the chemical attack claims to hinder the army's advances and provoke international military intervention.

The United Nations Security Council held a special meeting Monday to discuss what appeared to be a chemical attack, and US Ambassador to the United Nations Nikki Haley excoriated Russia , saying its hands are "covered in the blood of Syrian children."

"Russia could stop this senseless slaughter, if it wanted," she said. "But it stands with the Assad regime and supports it without hesitation."

Russia pushed back. "Nobody has invested you with the authority to act as gendarmes, policemen of the world ... we call on you to return to the legal fold," Ambassador Vassily Nebenzia said.

Despite the chaos in Douma, life goes on in the capital, Damascus. The streets are choked with traffic as people commute to work and marketplaces, while young people smoke shisha pipes at street-side cafes.

But there is also a sense of relief in the capital. Its residents have for years endured mortar fire from Eastern Ghouta, an enclave which Douma is part of, though that reprieve could be short lived.

President Trump on Sunday warned Russia, Iran and Syria of a "big price to pay" following the attack, and slammed Syrian President Bashar al-Assad as an "animal" on Twitter. On Monday he said the United States would respond in 24 to 48 hours.

"It was an atrocious attack, it was horrible, you don't see things like that as bad as the news is around the world, you just don't see those images," he said Monday.

The Organization for the Prevention of Chemical Weapons said that a fact-finding mission was working to establish whether chemical weapons were used.

Russian Foreign Minister Sergey Lavrov said Monday that his country had sent experts to Douma and that there was "no trace" of the use of chemical weapons there.

The attack came as Syrian forces were on the verge of reclaiming Douma, the last town held by rebels in Eastern Ghouta, which was besieged for six years and has been heavily bombarded since mid-February.

On Sunday, Syrian state TV reported that the government had reached an agreement with Jaish al-Islam, the only remaining rebel group in the town, to leave within 48 hours.

As part of the agreement, the group's fighters would be transported to Jarablus in northern Syria. In exchange, the rebels would release all captives they are holding in Douma.