The Turkish parliament has amended the constitution to allow the leader of the winning party at last month's general election to join parliament and so become prime minister.

Recep Tayyip Erdogan, the chairman of the AK Party, has been banned from running for parliament since 1999, when he was convicted on a charge of inciting religious hatred.

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He could win a seat as early as February, when an election will be re-run in a constituency in the south-east of the country.

But first the constitutional amendments must be signed into law by President Ahmet Necdet Sezer.

Mr Erdogan's candidacy must also be confirmed by the electoral board.

Ideological crime

The BBC's Turkey correspondent, Jonny Dymond, says Mr Erdogan's defeat in the election would be unthinkable, and that his supporters will now be in jubilant mood.

Turkey is a Muslim country but a secular state

For the past month, Turkey has had one of Mr Erdogan's deputies, Abdullah Gul, as prime minister, but power has clearly lain in Mr Erdogan's hands.

Mr Erdogan received a conviction because he recited a poem which refers to mosques as barracks and minarets as bayonets.

As a result, he was unable to stand for parliament - and only members of parliament are allowed to become prime minister.

Parliament has now changed the constitution to say that "ideological crimes" are no obstacle to elected office.

Legal battle

Of the 461 MPs present in the 550-seat house, 440 voted in favour of the amendments in a second and final round of voting, well above the necessary two-thirds parliamentary majority.

Although most Turkish citizens are Muslims, Turkey is a secular state.

The country's first Islamist government - formed by the AK Party's predecessor, the Virtue Party - was forced out of office by the military five years ago.

The AK Party says it is a modern conservative party, not an Islamist party, but it is still facing a battle to ban it in the courts.

After the party's election victory, Mr Erdogan said making progress with Turkey's bid to join the EU would be its top priority.

The by-election in which Mr Erdogan may stand is expected to occur on 9 February in Siirt.