BRUSSELS (Reuters) - The European Union will call on Zimbabwe's neighbours next week to step up pressure on President Robert Mugabe for the release of results of a March 29 election in which the opposition has claimed victory.

EU foreign ministers meeting next Tuesday will also pledge to explore how the 27-member bloc can use its diplomatic influence, according to a draft statement obtained by Reuters. Diplomats acknowledge EU leverage is limited.

"The (EU) Council remains concerned about the possible effects on the stability of the region as a consequence of the ongoing events and therefore calls upon SADC (Southern African Development Community) to engage with renewed determination with the Zimbabwean authorities," ministers will say.

SADC member countries include South Africa, Namibia, Mozambique, Zambia and others.

"The EU will ... explore further options for increasing pressure on those who direct and engage in state-sponsored violence and intimidation in the post-election period," the draft for the meeting in Luxembourg added.

EU diplomats said the ministers would stress the role of Zimbabwe's neighbours partly because the 27-member bloc has few options to apply pressure itself.

Existing EU sanctions include a ban on Mugabe travelling to parts of Western Europe. But that did not stop him from attending an EU-Africa summit in Lisbon last December that was boycotted by Gordon Brown, premier of ex-colonial power Britain.

Zimbabwe opposition leader Morgan Tsvangirai has said he won the presidential election outright and has accused Mugabe of delaying results to rig victory and keep his 28-year hold on power.

The EU statement noted the bloc remained Zimbabwe's most important donor and its willingness to resume full cooperation as soon as conditions allowed.