Miller: Pressure to quit increased

The move came after 27 MPs defected from the ruling Democratic Left Alliance to form a rival left-wing party, urging Mr Miller to step down.

There has been growing dissatisfaction within the party about its declining popularity, currently less than 10%.

Poland's President Aleksander Kwasniewski said he would propose a successor to Mr Miller by Monday.

Mr Miller announced his decision after meeting the president.

In the space of two-and-a-half years the party lost 4.5 million voters Marek Borowski Parliament speaker

"I informed the president that, taking all circumstances into consideration and using my constitutional rights, I will resign on 2 May," he told reporters.

He said he was resigning because Polish politics had become too divided and he no longer enjoyed people's trust.

The BBC's Adam Easton in Warsaw says the timing of the resignation appears to show Mr Miller has one eye on the history books.

He wants to lead Poland's celebrations as it enters the EU on 1 May, our correspondent says.

Earlier, parliament speaker and leading rebel Marek Borowski said the MPs had decided to split because "it was not possible to reform the party" and win back voters ahead of next year's elections.

"In the space of two-and-a-half years the party lost 4.5 million voters," he told a news conference.

But any government overhaul should not disturb Poland's smooth accession to the EU, he added.

EU requirements

High unemployment, a malfunctioning health care system and a string of high profile corruption scandals are seen as the main causes of Mr Miller's unpopularity.

Budget cuts introduced ahead of the country's EU membership, aimed at bringing its economy into line with EU requirements, have contributed to the problems.

Mr Miller stepped down as the leader of his party last month to concentrate on leading the country in the run-up to EU accession.

His resignation could trigger early parliamentary elections.