KINSHASA (BBC) -- The organization of the second round of the Democratic Republic of Congo's landmark elections has been thrown into confusion after a Supreme Court ruling.

The court ruled that the initial date for the run-off, 29 October, broke the constitution.

The shock ruling came as the two candidates in the second round held a two-hour meeting to ease tension.

The announcement of the first round results led to days of gun battles in Kinshasa, which left 23 people dead.

The 30 July election was the first democratic poll to be held in the country since it gained independence in 1960 and follows the official end of a five-year conflict. The United Nations is spending $1bn a year on its peacekeeping mission in DR Congo - the largest in the world. 'Long time'

The Supreme Court ruled that, according to the constitution, any second round must be held within 15 days of the announcement of the first round results.

Definitive results have not yet been declared but could be announced any day now, meaning the second round would have to be brought forward.

However, the election commission says it will appeal against the ruling, citing logistical difficulties in organizing polls at such short notice in a country two-thirds the size of Western Europe with very little infrastructure.

Election rivals President Joseph Kabila and Jean-Pierre Bemba met at the presidential palace in the capital, Kinshasa.

The talks were "very relaxed", Kabila's spokesman Kudura Kasongo told AFP but no further details of the discussions have been released.

There have been intense diplomatic efforts to bring the two men together.

European Union foreign policy chief Javier Solana and South African leader Thabo Mbeki have visited, appealing to them to settle their differences.

Bemba is a former rebel leader and retains his own personal security force. The presidential guard is widely regarded as Kabila's personal force.

In July's first-round of voting for a new president, Kabila took 45% of the vote, just short of the 50% needed for victory, while Bemba gained 20%.

Kabila won a landslide in the Swahili-speaking, war-ravaged east, where he is praised for bringing peace.

However, many in the Lingala-speaking west doubt Kabila's Congolese nationality and voted for Bemba.

The polls are meant to put an end to a transition process established after five years of war that ended in 2003.