ABUJA -- Nigeria's ruling Peoples' Democratic party (PDP) was close to victory last night in parliamentary elections, amid concerns about the potential for election violence and ballot rigging in Saturday's presidential poll.

The National Democratic Institute, the US-based election monitoring group, said last Saturday's parliamentary polls had unfolded more positively than expected but had still featured fundamental flaws threatening the credibility of the electoral process.

The comments reflect international anxiety over civilian rule in Nigeria, which has never had a successful transition between elected governments. "(This) is a rather clear, concise statement of our concern," said Patrick Merloe, the National Democratic Institute's director of electoral programmes. "Unless these things are done, the credibility of the process is placed in jeopardy."

President Olusegun Obasanjo's PDP, which dominated the last parliament, lost seats in the north to the main opposition All Nigeria People's party (ANPP) but made gains in the south-west at the expense of the Alliance for Democracy, its main rival in the region.

With 196 of the 360 House of Representatives seats counted, the PDP had 105 seats, while the ANPP had 60. In the 109-seat Senate, the PDP was ahead of its main rival by two to one.

The elections took place peacefully in many areas but polling-day violence left at least 10 people dead, and disrupted or stopped voting in parts of the oil-rich Niger Delta and elsewhere in the south.

Mr Obasanjo, a former military dictator whose election in 1999 ended more than 15 years of often brutal military rule, is seen as the frontrunner for the presidential poll, in which his main challenger is General Muhammadu Buhari, another former army ruler.

The National Democratic Institute said the security authorities and the Independent National Election Commission, the electoral regulator, needed urgently to address political intimidation and violations of ballot secrecy.

The International Republican Institute, the US-based group, reported "significant procedural irregularities".

"The worst fears of the Nigerian public and the international community did not occur," the institute said, although it added that weakness in the process could damage the "quality and efficiency" of the presidential election.

A Commonwealth election observer raised concerns about numerous logistical problems and violence between rival party members before and during the polls but said the most pessimistic predictions had been "confounded".