D66, led in the parliament by former MEP Lousewies van der Laan, had in a marathon nightly debate on Thursday morning demanded the resignation of hardline immigration minister Rita Verdonk over a row involving the Dutch nationality of Somali-born former member of parliament Ayaan Hirsi Ali.

Ms Hirsi Ali, who became known internationally through her battle against Islamic repression against women, gave a false name and story when entering the Netherlands as an asylum seeker in 1992.

Ms Verdonk last month said she would withdraw the Dutch passport of Ms Hirsi Ali, a move she had to reconsider in Thursday's debate through a face-saving legal manoeuvre which sparked D66's anger.

When Mr Balkenende refused to sack his immigration minister, the smallest coalition party withdrew political support for the cabinet.

D66 and most opposition parties demanded early elections, with the main opposition Labour party leader Wouter Bos saying, "The voters have to express themselves, preferably already in autumn," according to Dutch media.

But the two remaining ruling parties, Mr Balkenende's christian democrat CDA and the right-liberal VVD, have said they want to continue ruling as a minority government until the planned elections in May next year, possibly with the support of the rightist List Pim Fortuyn.

Possible autumn elections could see an early debate over the Netherlands' stance on the future of Europe after the Dutch voted "no" to the EU constitution last year.

All parties in the Dutch government agree the current text is "dead" but opinions diverge as to whether the Netherlands should hold a second referendum on any revised text.

The VVD, one of the parties supporting the referendum last year, appears to have got cold feet saying treaty changes should be ratified by parliament, but D66 and the Greens have already demanded a referendum on a new EU charter.

The party spearheading last year's "no" campaign, the Socialist Party (SP), is also likely to raise its voice over the issue in the election campaign.

The eurosceptic SP has been mooted as one possible coalition party for the Labour party in a possible new centre-left cabinet.