Countries that do not impose sanctions on Syrian President Bashar al-Assad's government are effectively allowing killings to continue, British Foreign Secretary William Hague said on Friday.

"There is no way of sitting on the sidelines on this," Hague told a meeting in Paris of the Western and Arab states that backa rebel uprising against Assad and want him out of power.

"If you don't impose sanctions and implement them thoroughly you are allowing the provision to the Assad regime of the means to go on killing the Syrian people," Hague said.