Mr Schori flew into London on Sunday after his visa was cancelled.

About 30 observers from the EU are currently in Zimbabwe.

The EU had for weeks been threatening to impose targeted sanctions - including a travel ban and a freeze on assets - against President Robert Mugabe and 19 other senior officials, if the Zimbabwe Government hampered the work of the EU's election observer mission.

The measures come just weeks ahead of hotly contested presidential elections in Zimbabwe amid rising political violence.

In the Zimbabwe capital Harare on Monday, hundreds of Mr Mugabe's supporters attacked the headquarters of the main opposition party, the Movement for Democratic Change (MDC), throwing stones and smashing windows.

Riot police arrested dozens of protesters, witnesses told Reuters news agency.

'Unprecedented move'

EU ministers said in a statement after the Brussels meeting that Mr Mugabe's government had "prevented the deployment of an EU observation mission".

"The EU remains seriously concerned at political violence, serious violations of human rights and restrictions on the media... which call into question the prospects for a free and fair election," the statement said.

UK Foreign Secretary Jack Straw said the sanctions were designed to hit the political elite, not the economy, because Mr Mugabe had already damaged that.

They would include a ban on travel to the EU, a freeze on financial assets held there and an arms embargo.

However, aid projects such as educational work would not be affected.

Expressing regret at the pull-out, EU External Affairs Commissioner Chris Patten said the EU had concluded that leaving even a small number of EU observers "would have played into Mr Mugabe's hands".

"Our argument is not with with the people of Zimbabwe, but with Mugabe and his cronies."

He added that the EU backed the continuing missions in Zimbabwe fielded by African countries, Norway and others.

Zimbabwe hits back

The announcement of the sanctions brought criticism from Zimbabwe.

Justice Minister Patrick Chinamasa castigated the EU, accusing it of wanting to impose its will on Africa and Africans.

"This generation of Africans will not want to be owned... There is no basis in international law to seek to impose themselves as observers," he told the BBC.

Meanwhile the human rights group Amnesty International expressed regret about the departure of EU observers, saying although it understood the reasons for the withdrawal "we think it would have been better for them to stay".

Regional support

Mr Mugabe, who insists the election will be free and fair, has been seeking to enlist the support of other African leaders in the face of allegations of violence and intimidation against his political opponents.

He justified the expulsion of Mr Schori when he met other African leaders on Sunday in Mozambique, describing Mr Schori, a Swede, as an "uninvited guest" to Zimbabwe's "election banquet".

Mr Schori said he had been expelled on "false grounds" in an unprecedented move against the head of a monitoring team.

Mr Mugabe's government accuses Britain, Denmark, Finland, Germany, the Netherlands and Sweden of supporting the opposition.

The South African Development Community (SADC) was due to send its own election observers to Zimbabwe on Monday.

But it has been accused by Zimbabwean opposition leader Morgan Tsvangirai of backing Mr Mugabe.