U.S. President Barack Obama and British Prime Minister David Cameron could tighten sanctions against Syria to increase the pressure on president Bashar Assad, the Prime Minister’s spokesman said, according to UKPA.

The spokesman said the Prime Minister and the U.S. president were "disappointed" at the failure earlier this month to agree a United Nations Security Council resolution (UNSCR) condemning the regime's brutal crackdown on anti-government protesters who took to the streets 10 months ago as popular uprisings swept the Arab world.

The pair have previously called on Assad to step down, and they talked about the latest violence in a transatlantic phone call on Monday, Feb 13 night.

According to the spokesman, "The leaders expressed disappointment at the Russian and Chinese vetoes of the draft UNSCR on February 4. They agreed on the need for international unity against the regime's attacks on its own citizens, including further action at the UN and a broad and strong coalition in the new Friends of Syria group. They discussed the possibility of increasing the pressure on the Assad regime through additional sanctions."