WASHINGTON (AP) — U.S. intelligence officials are still trying to determine whether Syrian President Bashar Assad unleashed a deadly chemical weapons attack against his people earlier this week.

That's the word from the White House after President Barack Obama met with his national security team Saturday to discuss possible next steps in Syria. Officials have said Obama will decide how to respond once the facts are clear.

A statement from the White House about Saturday's meeting said Obama also received a detailed review of the range of options he has requested for the U.S. and its international to respond if it is determined that Assad has engaged in deadly chemical warfare.

The White House says Obama and British Prime Minister David Cameron also discussed the situation in Syria by telephone Saturday.

Meanwhile, the Syrian government is accusing rebels of using chemical weapons and is warning the United States not to launch any military action against Damascus over an alleged chemical attack last week, saying such a move would set the Middle East ablaze.

The regime of President Assad made the accusations against opposition forces at the same time an international aid group says it has tallied 355 deaths from a purported chemical weapons attack on Wednesday in a suburb of the Syrian capital.

Meanwhile, U.S. naval units are moving closer to Syria as President Barack Obama considers a possible military response.

U.S. defense officials say the Navy had sent a fourth warship armed with ballistic missiles into the eastern Mediterranean Sea but without immediate orders for any missile launch into Syria. The officials spoke on condition of anonymity because they weren't authorized to discuss ship movements publicly.