Jack Straw has asked the US to back a decision by Europe's foreign ministers to impose sanctions on Zimbabwe and to pull out EU observers attempting to promote free and fair elections in the country.

Thirteen out of the 15 EU ministers - including Britain - and the European Commission backed sanctions against Zimbabwe's ruling Zanu PF party and president Robert Mugabe from the outset. They also decided to withdraw 30 election observers following the ejection of EU election monitoring chief, Pierre Schori, at the weekend.

Following the meeting the UK foreign secretary spoke to US secretary of state Colin Powell and urged him to back the EU sanctions.

The sanctions will have immediate effect with a travel ban on Mugabe and about 20 of his close political associates. Their assets in EU countries will also be frozen

Schori addressed the ministers as they decided whether it was worth keeping the monitors in place - preserving a semblance of influence over the conduct of the election - or whether they should introduce "smart sanctions" targeting Zimbabwe's rulers.

Straw stressed that the sanctions would be focused on Zimbabwe's government and not the country's ordinary people and warned that allowing EU observers to remain could "provide a veneer of respectability if Mugabe succeeded in his quest to steal the election''.

"In no sense are these economic sanctions against the people of Zimbabwe. That has never been the issue. We all took the view that president Mugabe has done quite enough damage to the prosperity and economy of Zimbabwe without us adding to it," he said.

Most believed that following the expulsion of Schori sanctions were inevitable, but Greece and Portugal warned that maintaining the observation mission was more important than "macho" interventions that could further wreck the elections in the crucial run-up period and provoke the charge that Europe was interfering in Africa's affairs.