British Foreign Secretary Jack Straw said on Tuesday it was up to Syria to prove it was no 'rogue nation' by providing answers to charges that it took in fleeing leaders of the overthrown Iraqi government.

"Syria has an opportunity to prove that it's not in that category," he told a news conference at the Qatar Central Command headquarters running the war in Iraq.

"We look forward to them understanding this new reality and moving forward."

The United States ratcheted up pressure on Damascus on Monday by threatening sanctions over charges that it was harbouring Iraqi leaders, developing chemical weapons and supporting terrorism.

US Defence Secretary Donald Rumsfeld accused Syria of carrying out tests involving chemical weapons over the past 12 to 15 months.

Syria denied all the charged.

US officials stopped short of threatening to extend the Iraq war into Syria, but insisted all options remain on the table.

Analysts doubted Washington would launch military action, and expect it to use diplomatic pressure to try to persuade Syrian President Bashar al-Assad to change course.

"There are some important questions for Syria to deal with… which include the question of chemical weapons.

"We in the United Kingdom have tried to improve relations with Syria. There is an agenda for Syria and it's important that they take it in a constructive way." 

He denied the United States and Britain had lined up a list of countries against which they were planning military action.

"There isn't a list, and Syria isn't on it," he said. "But Syria has got to understand the seriousness of this situation."