WARSAW, Poland — Prime Minister Leszek Miller stepped down Sunday after helping lead Poland into the European Union, his government weakened by unresolved economic problems, corruption allegations and a split in the governing party.

After receiving Miller's resignation, President Aleksander Kwasniewski was to appoint former finance minister Marek Belka as new prime minister in a ceremony at the presidential palace.

Coming the day after Poland's historic entry into the EU, Miller's handover to a caretaker underscores the domestic uncertainty afflicting a key U.S. military ally in Iraq.

Miller said he was proud to have attained EU membership, the most important target he set for his administration.

"I am proud to have headed a government which has achieved what seemed impossible," Miller said in a speech, after which he and Kwasniewski shook hands and hugged.

Kwasniewski has expressed faith that Miller's departure will help stabilize Poland, but it's unclear whether Belka will gain the support in parliament to bring down a staggering budget deficit and unemployment that has topped 20 per cent.

Belka's appointment is not expected to affect Poland's continued leadership of a multinational force of around 9,000 troops in Iraq.

Approval ratings for Miller's government -- the eighth since communism fell 15 years ago -- have hit all-time lows as he pushed social spending cuts to prepare Poland for the EU.

Allegations of corruption among government officials and a botched health care reform also undermined Miller.

Belka is respected in the business community for his support of fiscal austerity. But to soften his image, he has promised lately to make jobs and health care reform a priority.