William Hague has hailed the UN Security Council's decision to step up its monitoring of the volatile ceasefire in Syria.
The foreign secretary said the move - which could see the number of observers boosted from 30 to 300 - intensified pressure on the regime to reform.
But he reiterated his concerns that president Bashar Assad's government was still not abiding by its commitments under the peace deal.
The resolution gives UN Secretary General Ban Ki-moon authority to deploy the additional monitors as he sees fit to consolidate the ceasefire.
The text was passed unanimously after European nations dropped their insistence on a threat of non-military sanctions if Syria failed to withdraw troops and heavy weapons from towns and cities.
In a statement, Mr Hague said: "This resolution increases the pressure on the Syrian regime to begin a transition to a democratic, plural political system. I welcome the fact that the Council reaffirmed its full support for this goal.
"However, I remain extremely concerned that the Syrian regime is still failing to meet its commitments, and that there has been further violence and the use of heavy weapons since April 12 when a ceasefire should have come into effect.
"The Syrian regime must stop immediately troop movements towards population centres; end the use of heavy weapons in civilian areas; and withdraw the military to their barracks. The Syrian regime must ensure that the UN monitoring mission can operate freely and safely, and this must include agreement on the use of air assets.
"If the Syrian regime fails to take these steps and to comply with Kofi Annan's plan in full, we will push for further action, including in the UN Security Council."
Mr Ban has accused president Assad of failing to honour the ceasefire, and expressed dismay at an upsurge in violence.
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