Mr Rasmussen is widely expected to win again

The party, led by Prime Minister Anders Fogh Rasmussen, has been in power since November 2001. It governs in a coalition with the Conservative Party.

Under the constitution, the prime minister can set an election date at any time during the government's four-year term.

Opinion polls indicate that the ruling coalition will win.

The centre-right government has tightened Denmark's immigration laws and supported the US-led war that toppled Iraqi President Saddam Hussein.

Denmark has 525 troops in Iraq, and correspondents say a change of government would be unlikely to lead to their early withdrawal.

Like the UK, Denmark has stayed out of the eurozone.