KUALA LUMPUR - Malaysia's ruling party, which is being overhauled after an electoral setback, faced fresh controversy Thursday as outgoing premier Abdullah Ahmad Badawi's son-in-law was elected to a key post.

Abdullah stepped down as leader of the United Malays National Organisation (UMNO) Thursday, after a disastrous performance in elections a year ago that handed the opposition an unprecedented one-third of parliamentary seats.

He was replaced by his deputy Najib Razak, who has called for a radical revamp to reverse UMNO's reputation for being corrupt and out of touch with voters, and the installation of a strong new leadership team.

As the party votes this week for a range of top positions up for grabs, Abdullah's son-in-law Khairy Jamaluddin was thought to be out of the running in his bid to be chief of the youth wing -- a nurturing ground for future leaders.

Pundits said he was seen as having too much influence over Abdullah and partly to blame for the disastrous polls, and his prospects were further damaged when he was rapped over vote-buying.

But in a shock result announced late Wednesday, he won by a narrow margin, edging out other candidates including the son of former premier Mahathir Mohamad who ruled for two decades until 2003.

In a victory speech, Khairy promised not to punish those who campaigned against him, and called on the youth wing to unite and "stand by me when we meet the opposition, wherever they are."

"Some had said that 'He is finished without his father-in-law. He is gone.' But I returned to the basics of UMNO politics. I built comradeship with the grassroots," he said.

However, as he left the hall, dozens of disgruntled members began booing him and accusing him of corruption. Some 50 police were quickly deployed to secure the area and bustle Khairy out through another exit.

Foreign Minister Rais Yatim called for further investigation into the affair.

"The UMNO majority voice has spoken but there seems to be a disgruntled situation where people were talking about corruption against Khairy," he told AFP.

"Since the commotion was substantial we should not ignore it and therefore the (UMNO disciplinary committee) should take a good fine tooth comb and go through it."

The Oxford-educated Khairy was an aide to Abdullah before marrying the boss's daughter in 2001, sending him on a meteoric rise that landed him the deputy youth chief position in 2004.

The contest against Mukhriz Mahathir, a 44-year-old businessman, was seen as determining which of Malaysia's top political clans will control its future after the two patriarchs had a very public falling out.

In another high-profile contest, former cabinet minister and political veteran Rafidah Aziz was knocked out as leader of UMNO's women's wing, in favour of her former deputy Shahrizat Jalil.

Shahrizat is also seen as close to Abdullah, potentially creating problems for Najib who inherits a party leadership packed with allies of his predecessor who is being forced out reluctantly.

"Khairy's win was an upset, and there's a big question mark over whether he can hold the youth movement together, it's not going to be easy for him," said political analyst Khoo Kay Peng.

"It has disrupted the power balance within Najib's team. He definitely wanted people from his own faction," he added.