British foreign secretary William Hague says all options are on the table to resolve Syria crisis as he calls for more pressure on Damascus to abide by the Annan peace plan, with or without UN resolution.

"It is right to continue to seek a peaceful solution. But of course, the situation is deteriorating so gravely and that we do have to do other things. In the United kingdom for instance, we have continued to increase support and non-lethal support for the opposition, to apply more sanctions to Syria. We look to other countries to do the same, with or without the United Nations resolution and the situation is so grave and so unpredictable that I do not think that any option should be ruled out for the future," Hague said.

China and Russia have previously vetoed resolutions designed to pressure Syrian President Bashar al-Assad, but say they are committed to the peace plan drafted by U.N. envoy Annan which proposes national dialogue.

On Iran's nuclear programme, Hague said more sanctions would be enforced against Tehran if no diplomatic progress is achieved.

"We have brought into force very wide ranging sanctions on Iran, without progress in these negotiations, we will intensify these sanctions in the months ahead. We are determined to prevent a nuclear proliferation in the Middle East and the Iranians should not doubt our resolve and determination to prevent that coming about," Hague added.

Iran denies Western accusations of a covert agenda to develop a nuclear weapon, insisting it wants to stockpile enriched uranium solely to generate more electricity for a rapidly growing population and radio isotopes for medical use.

Talks between world powers and Iran to resolve the standoff have so far failed to secure a breakthrough.