Making his case at the White House on Monday, U.K. Prime Minister David Cameron said the only way a political solution to the Syrian civil war will survive is to guarantee opposition forces can "withstand the onslaught" by forces loyal to Syrian President Bashar Assad.
Cameron's call to action on Monday echoes those by Congress who, in recent weeks, have turned up the pressure on President Obama to take military action to end the three-year war in Syria.
Rebel troops have so far been unable to match Assad's heavy weapons and air power, supplied by Russia and Iran, used to batter opposition forces looking to topple the longtime leader.
The suspected use of chemical weapons by the Assad regime against rebel forces crossing a "red line" set by President Obama, has further fueled congressional calls for U.S. action.
Sens. John McCainJohn McCainSenate committee to vote Monday on Tillerson Trump fails to mention Clinton in inaugural address Hillary Clinton under microscope at inauguration MORE (R-Ariz.), Lindsey GrahamLindsey GrahamThe Hill's 12:30 Report Graham: Trump would make mistake in not punishing Russia Graham to vote for Trump’s EPA pick MORE (R-S.C.) and Senate Armed Services Committee chief Carl LevinCarl LevinObama to preserve torture report in presidential papers 'Nuclear option' for Supreme Court nominees will damage Senate McCain's Supreme Court strategy leads to nuclear Senate MORE (D-Mich.), have spearheaded those calls for U.S. intervention — including using American warplanes against Assad targets and supplying heavy weapons to rebel forces.
Senate Foreign Relations Chairman Robert MenendezRobert MenendezCarson likely to roll back housing equality rule Live coverage: Tillerson's hearing for State Booker to join Foreign Relations Committee MORE (D-N.J.) recently introduced legislation to arm and train opposition forces in Syria that have been vetted by U.S. military and intelligence officials.
But the Obama administration has balked at such efforts, concerned American weapons could end up in the hands of Islamic terror groups, including al Qaeda affiliates in Iraq and Syria that are fighting alongside opposition troops.
In March, France abandoned its support for arming Syria's rebels, further splintering the already fractious support among Western European powers to take a more direct role in ending the war.
While Cameron made clear he had not made a decision to arm rebel troops, London continues "to examine and look at the E.U. arms embargo and see whether we need to make further changes to it in order to facilitate our work with the [Syrian] opposition," he said.
Currently, all British forces are providing is "technical assistance and advice" to opposition leaders, as well as providing non-lethal aid — including armored vehicles and body armor — to Syrian rebel units, according to Cameron.
For their part, the Pentagon is providing training and assistance to Jordan and Turkey, including setting up Patriot anti-missile batteries along the Syrian-Turkish border, to keep the war from spilling into those countries.
But that may still not be enough to turn the tide of the war toward the rebels, Cameron said.
"I do believe that there's more we can do alongside technical advice, assistance, help in order to shape them, in order to work with them," he said.
"If we don't help the Syrian opposition who we do recognize as being legitimate ... then we shouldn't be surprised if the extremist elements [inside Syria] grow," Cameron added.