US Secretary of State John Kerry said on Friday that President Barack Obama had again asked for policy options on Syria but that none have yet been presented to him.
Kerry told reporters Obama was concerned about the deterioration in the humanitarian situation in Syria and also by the fact that peace talks between the opposition and government had not produced a discussion of a transitional government as had been planned.
As a result, Kerry said, "he has asked all of us to think about various options that may or may not exist."
"The answer to the question: have they been presented? No, they have not. But that evaluation, by necessity, given the circumstances, is taking place at this time," Kerry said. "And when these options are ripe and when the president calls for it, there will undoubtedly be some discussion about them."
White House spokesman Jay Carney said in Washington that Obama expected his national security team to constantly re-evaluate policy options on Syria and other issues.
"Secretary Kerry was reiterating what has always been the case, which is that the president is always looking at options on policy matters like Syria," Carney said. "This is not a one-time thing. It's not like this is a new review."
Also on Friday, a car bomb killed at least 18 people a town in southern Syria, the Syrian Observatory for Human Rights reported.
The bomb went off near a mosque in the town of al-Yadouda near the border with Jordan, Rami Abdulrahman, director of the Observatory, said by phone.
Car bombs are commonly deployed as a weapon in the three-year old Syrian conflict.
The Observatory said earlier this week that since peace talks between the Syrian government and opposition leaders began in Geneva some three weeks ago, Syrians had died at the fastest rate since the country's civil war erupted.
Meanwhile the Syrian Observatory also reported Friday that an al-Qaida splinter group in Syria executed at least 13 people including relatives of fighters from rival rebel groups before withdrawing from a town near Aleppo.
The London-based monitoring group said the men killed by the Islamic State of Iraq and the Levant militants included rebels who were detained by ISIL after laying down their arms. The Observatory said their bodies had been thrown into a well.
It did not say when the incident took place in Haritan, just northwest of Aleppo, one of the most contested areas in an almost three-year-old civil war between insurgents and the forces of Syrian President Bashar Assad.
Several Islamist and more secular rebel factions joined forces in January for an offensive to try to push their former ISIL allies out of rebel-held regions in northern and eastern Syria.
ISIL, which has attracted many foreign militants into its ranks, is a small but powerful fighting force in Syria and also operates in neighboring Iraq. It has alienated many civilians and opposition activists by imposing harsh rulings against dissent, even beheading its opponents, in areas it controls.