Hammond met in Washington with U.S. Defense Secretary Chuck Hagel to discuss options to end the war in Syria.
Syria's three-year war has left at least 70,000 people dead and more than 1 million displaced.
Hammond said diplomacy was the preferred option for ending the conflict, adding that Syrian President Bashar Assad has no place in a future Syria.
"We in the U.K. are stepping up our support to the national coalition and remind the regime that nothing has been taken off the table in the light of the continuing bloodshed," he said.
NATO forces deployed missile defense systems in Turkey to prevent the Syrian war from spilling across the border. NATO defense ministers said there are no plans to set up a no-fly zone over Syria, however.
Hagel said supplying anti-government forces with weapons is one of the options under consideration.
"Any country, any power, any international coalition, any partnership is going to continue to look at options, how best to accomplish those objectives," he said.
Arming opposition forces comes with risks as some of those groups have ties to al-Qaida.