(Adds Yala rejects results, says police tried to arrest him)

BISSAU, Nov 21 (Reuters) - Guinea-Bissau's former ruling party won a clear majority in last weekend's parliamentary election, seeing off a new formation allied to President Joao Bernardo "Nino" Vieira, provisional results showed on Friday.

The African Party for the Independence of Guinea-Bissau and Cape Verde (PAIGC) won 67 of 100 National Assembly seats, according to results announced by National Electoral Commission head Aladji Malam Mane.

Opposition chief Koumba Yala, a former president overthrown in a 2003 coup who has called for the U.N. Security Council to investigate drug-trafficking during Vieira's rule, rejected the results and said police tried to arrest him on Friday.

The PAIGC, a former independence movement which quit a unity government in July after its representatives were sacked from top financial jobs, had asked voters for a mandate to rule.

Foreign aid donors hope the election will help counter unrest in the poor and volatile West African country, which crime-fighters fear is becoming a "narco-state" under the influence of Latin American cocaine-smuggling gangs.

Yala, the head of the Social Renewal Party (PRS) who won a presidential election in 2000 after a brief civil war, said the results of Sunday's poll were rigged.

The PRS, which draws its strength from the Balante ethnic group and is backed by military chiefs, emerged as the second party in parliament with 28 seats.

Yala said heavily armed members of an elite police unit had tried unsuccessfully to arrest him in the town of Bissoran, 80 km (50 miles) northeast of the capital Bissau, late on Friday after the results were announced.

"I will never accept fabricated results, because my party is stronger than ever," he said.

BOUTS OF VIOLENCE

Yala has said voting materials were not supplied to several places where he has support, including Bissoran.

Interior Minister Armando Nhaga's spokesman accused Yala of trying to leave the country after the election.

"Koumba Yala will not leave Guinea-Bissau until he proves his accusations that the head of state, Nino Vieira, is involved in drug trafficking," the spokesman said.

Guinea-Bissau has suffered frequent bouts of violence since independence from Portugal in 1974 and crime and security experts believe drug trafficking is aggravating instability.

International election monitors have said the elections were calm and well organised. Mane said turnout was 82 percent.

The upstart Republican Party for Independence and Development (PRID), led by Vieira's ally and former Prime Minister Aristides Gomes, won just three seats. Two minor parties won one seat each.

"The elections went well, we are happy," said petrol station attendant Sherif Seidi. "I hope (PAIGC leader) Carlos Gomes Junior will help the country. We are asking him to relieve the suffering of the people."

Guinea-Bissau is one of world's poorest countries.

"This is the result we have waiting been for," said Bissau resident Alex Yala. "This country wants peace and stability, so poverty can be relieved."

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