US Ambassador Samantha Power lashed out at Russia at the UN on Thursday, accusing Moscow of holding the Security Council “hostage” by blocking action against Syria.

Power said: “The system has protected the prerogatives of Russia, the patron of a regime that would brazenly stage the world’s largest chemical weapons attack in a quarter century, when chemical weapons inspectors sent by the UN were just across town.”

The Navy’s top admiral said the four US destroyers off the coast of Syria are “fully ready” for a wide range of possible action.

Adm. Jonathan Greenert, the chief of naval operations, said Thursday that the US ships are prepared for what he called a “vast spectrum of operations,” including launching Tomahawk cruise missiles at targets in Syria and protecting themselves in the event of retaliation.

Greenert’s role is to ensure that naval forces are properly trained and equipped; he is not in the chain of command.

The Navy says the Tomahawk missiles that could be launched by the destroyers in the eastern Mediterranean cost $1.5 million each.

British Prime Minister David Cameron said British scientists have found new evidence that poison gas was used outside Damascus. Cameron told BBC that samples from Syria had been examined by experts at England’s Porton Down Laboratory.

The Kremlin’s chief of staff said Russia has been sending warships to the Mediterranean Sea for possible evacuation of Russian citizens from Syria.

A top official said Russia has been boosting its naval presence in the Mediterranean “primarily” in order to organize a possible evacuation of Russians from Syria.

Barack Obama’s advisors were pressing Congress on Thursday, this time in closed-door meetings, for its authorization of a military strike on Syria, while the president arrived at a G-20 summit to certain questions and skepticism from other world leaders. That includes the event’s host, Russian President Vladimir Putin. Obama and Putin shared a 15-second greeting.

World leaders were locked in a divisive debate over Syria, at the end of the first day of the G-20 summit.

Opening the summit, Putin confirmed Syria would be discussed at the working dinner, despite not being on the agenda.

Meanwhile, Assad’s former defense minister has reached Istanbul after a defection that betrays cracks in the president’s support among his own Alawite sect, opposition and diplomatic sources said on Thursday.

Dismissing a cursory Syrian state television denial of the first Reuters report that Gen. Ali Habib had been spirited across the Turkish frontier this week, opposition figures said Habib was likely to keep a low profile.

Pope Francis, meanwhile, urged the Group of 20 leaders to abandon the “futile pursuit” of a military solution in Syria as the Vatican laid out its case for a negotiated settlement that guarantees rights for all Syrians, including minority Christians.