US Ambassador to the United Nations Nikki Haley warned on Monday that Washington ‘remains prepared to act if we must,’ if the U.N. Security Council fails to act on Syria, as the Syrian army’s onslaught in eastern Ghouta continued unabated.

The United States asked the Security Council to demand an immediate 30-day ceasefire in Damascus and rebel-held eastern Ghouta, where Syrian President Bashar al-Assad’s forces, backed by Russia and Iran, say they are targeting ‘terrorist’ groups which are shelling the capital.

The army’s onslaught in eastern Ghouta, backed by air and artillery strikes, has killed about 1,160 people since Feb. 18, a war monitoring group said, as Assad seeks to crush the last big rebel stronghold near the capital Damascus.

‘It is not the path we prefer, but it is a path we have demonstrated we will take, and we are prepared to take again,’ Haley told the 15-member Security Council. ‘When the international community consistently fails to act, there are times when states are compelled to take their own action.’

The United States bombed a Syrian government air base last year over a deadly chemical weapons attack.

The Security Council demanded a 30-day ceasefire across Syria in a unanimously adopted Feb. 24 resolution.

Russia and Damascus say a ceasefire ordered by the U.N. Security Council does not protect the fighters in eastern Ghouta, arguing that they are members of banned terrorist groups.

‘There has been no cessation of hostilities,’ U.N. Secretary-General Antonio Guterres said on Monday. ‘Violence continues in eastern Ghouta and beyond - including in Afrin, parts of Idlib and into Damascus and its suburbs.’

‘No sieges have been lifted ... To our knowledge, not one critically sick or wounded person has yet been evacuated.

Russia’s U.N. envoy Vassily Nebenzia also said some states were accusing the Syrian government of carrying our chemical weapons attacks in a bid to ‘prepare the ground for the unilateral use of force against sovereign Syria.’

‘We have heard hints of that in the statements of some delegations today,’ Nebenzia said. ‘Basically steps are being weighed which could hit regional stability very, very hard.’

Elsewhere, Syrian jets also struck rebel-held towns in the country’s south, the first aerial attacks on the area since the United States and Russia brokered a deal making it a ‘de-escalation zone’ last year, rebels and residents said.

The Trump administration frequently points to the de-escalation zone as a sign of progress it can achieve with Moscow on reducing the violence in Syria. But on Monday, the US State Department said it was very concerned by the violence and called an ‘urgent meeting’ in Jordan to ensure maintenance of the de-escalation zone.

‘If (reports of the strikes are) true, this would be a clear violation of the (southwest) ceasefire by the Syrian regime that broadens the conflict,’ a State Department official said.

‘We urge all parties in the southwest de-escalation zone not to take actions that would jeopardize the ceasefire and make future cooperation more difficult.’