The US Pentagon was preparing military options for Syria on the request of President Barack Obama, the chairman of the Joint Chiefs of Staff General Martin Dempsey told the Senate on Wednesday.

The various options for the country that is the scene of a bloody government crackdown on the opposition have however not been discussed with Obama or his security advisors, he said.

Dempsey was speaking before the Senate Armed Services Committee against the backdrop of calls from senators for US military intervention in the Middle Eastern country.

Addressing the committee, Defence Secretary Leon Panetta warned that US military intervention would be “a mistake” and would risk fuelling a civil war.

The Pentagon chief called on the Senate to “recognize the limitation of military force, especially US boots on the ground.”

Both Panetta and Dempsey warned that airstrikes would lead to civilian casualties. They also noted that the situation in Syria could not be compared with that of Libya, where the international community imposed a no-fly zone.

Syria’s air defence system was five times more advanced than that of the North African country, which means a sustained air campaign with a large number of aircraft would be required.

On Monday, former Republican presidential candidate John McCain became the first senator to call for such military action against the security forces of Syrian President Bashar al-Assad. This, McCain said, would be the “only realistic way” to end the bloodshed.