President Obama called British Prime Minister David Cameron Saturday afternoon to discuss the Syrian government’s reported use of chemical weapons against civilians in Damascus and to weigh a possible military response.

During the phone call, the two leaders voiced their “grave concern” about the reported chemical attacks and pledged to continue to consult closely about a potential response by the international community, according to a White House readout of the phone call.

“The United States and UK stand united in our opposition to the use of chemical weapons,” the White House said in the statement.

The U.S. intelligence community continued to “gather facts” about the reported chemical attack as Obama met with his National Security Council Saturday and received a “detailed review of a range of potential options he had requested be prepared,” the White House said.

Obama so far this week has avoided the use of the term “red line” – a warning he has repeatedly voiced in the past – in describing reports of the Syrian government’s use of chemical weapons. Instead, he called reports of a chemical assault killing hundreds of civilians and affecting thousands more “troublesome” in an interview with CNN on Friday.

With the U.S. and its allies on edge about the reports, Obama moved U.S. naval warships closer to Syria in preparation for a possible strike. He also spent Saturday reviewing dozens of witness accounts of the chemical use, as well as records of the symptoms of those killed.