Ukraine's ongoing political crisis took another unexpected turn, when late-night talks involving international mediators broke up without an expected compromise deal. Parliament is to convene, later today, amid continuing uncertainty about what comes next.

Marathon talks ended early Tuesday, with the two sides in Ukraine's election dispute failing to agree on the issue of whether to weaken the powers of the presidency, as the current government wants.

Earlier, both sides indicated a compromise deal was in the works that would allow for constitutional changes, as well as new electoral laws to ensure a free-and-fair vote on the fresh runoff election, December 26.

Opposition leader Viktor Yushchenko says such changes are essential to avoid a repeat of the November 21 election, which the supreme court has declared invalid because of fraud.

President Leonid Kuchma insists that - as a first step - the opposition must agree to constitutional changes that will transfer many presidential powers to parliament.

Mr. Yushchenko says the authorities favor this because they realize he will be the winner of the December 26 runoff.

Another sticking point is Mr. Yushchenko's demand that Mr. Kuchma dismiss his presidential rival, Prime Minister Viktor Yanukovich, who insists he will be a candidate in the new runoff vote, despite signs he is losing Mr. Kuchma's backing.

The Ukrainian president has even suggested that Mr. Yanukovich might well withdraw from the race.

The two sides did agree on the need to replace the electoral commission that had announced the results of the last election.

Mr. Kuchma says he will submit names for a new commission at a special session of parliament, later Tuesday. However, the breakdown of a final compromise deal now casts a shadow over the new legislative session.

The Tuesday-morning talks marked the third time international mediators had come to Ukraine, trying to end the political standoff.

The presidents of Poland, Lithuania, the European Union foreign policy chief and the speaker of Russia's parliament were all present at the nearly-six-hour negotiating session.

Ukraine's election dispute has caused friction in relations between Russia and Western nations, after President Vladimir Putin openly backed Mr. Yanukovich, despite evidence of fraud.

Although continuing to criticize what he calls "Western meddling" in Ukraine, Mr. Putin says he will work with whomever becomes the country's new leader.