KUALA LUMPUR (Reuters) - Malaysian Prime Minister Najib Razak said on Saturday the political opposition would be given an oversight role over the country's Election Commission, a move aimed at healing divisions following a disputed May 5 election.

The opposition has held a series of rallies around the country as it refuses to accept the ruling coalition's victory, saying it was tainted by widespread fraud that the Election Commission (EC) has failed to address.

The opposition has long said the commission is biased towards the Barisan Nasional coalition, which extended its 56-year rule in the election but saw its parliamentary majority reduced. It lost the popular vote for the first time in 44 years.

The commission rejects the accusations of bias and says the election was fair.

Najib, in a speech to mark the Malaysian king's birthday, announced that an independent, bipartisan parliamentary committee made up of government and opposition members would be formed to oversee the Election Commission.

"I understand that sections of the public want to see our election processes strengthened," said Najib.

"I am announcing these improvements to our electoral system in the spirit of unity and national reconciliation."

The opposition gave a cautious welcome to the announcement but reiterated its demand that the EC's leadership should resign.

The opposition alliance, led by a former deputy prime minister, Anwar Ibrahim, is preparing to mount a legal challenge to the results in nearly 30 close-run seats.

"The Election Commission needs a clean start," Lim Kit Siang, a senior opposition politician, told Reuters.

"There is no doubt that the EC has in many instances acted as a Barisan Nasional protagonist in attacking opposition leaders, rather than acting under an impartial rule."

(Reporting by Anuradha Raghu,; Editing by Stuart Grudgings and Robert Birsel)