UNITED NATIONS - US Ambassador to the United Nations Nikki Haley warned on Monday that if the U.N. Security Council fails to act on Syria, Washington "remains prepared to act if we must," just as it did last year when it bombed a Syrian government air base over a deadly chemical weapons attack."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."Haley's warning came as 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 Security Council demanded a 30-day ceasefire across Syria in a unanimously adopted Feb. 24 resolution. Russia had said the Security Council could not impose a ceasefire without a deal between the warring parties.UN Secretary-General Antonio Guterres briefed the council on Monday on the implementation of the resolution."There has been no cessation of hostilities," Guterres said. "Violence continues in eastern Ghouta and beyond - including in Afrin, parts of Idlib and into Damascus and its suburbs.""Despite some limited convoy deliveries, the provision of humanitarian aid and services has not been safe, unimpeded or sustained," Guterres said. "No sieges have been lifted ... To our knowledge, not one critically sick or wounded person has yet been evacuated."Thousands of families are sleeping in the open in the streets of the biggest town of Syria's rebel-held eastern Ghouta enclave, where there is no longer any room in packed cellars to shelter from government bombardment, local authorities said.