Former Umno leader Mahathir Mohamad, who tightly controlled the Malay nationalist party for 22 years, was on the receiving end of attacks by the party yesterday, as its leaders poured scorn on his decision to join the opposition and his continuing calls for Prime Minister Najib Razak to resign.

"What's saddest to me is when our former leader is in alliance with the opposition. The day he sat and 'kissed' Lim Kit Siang is the darkest day of my life," said Umno Women chief Shahrizat Abdul Jalil, referring to Democratic Action Party's veteran leader, Mr Lim.

Umno's top echelons were united in their speeches condemning Dr Mahathir's move to join the opposition, including a much-reported handshake with his former deputy prime minister and political nemesis Anwar Ibrahim.

Umno Puteri (young women) chief Mas Ermieyati Samsudin added another dimension. She said Malaysians who work with foreigners like American financier George Soros are traitors, repeating the oft-made claim by officials that Mr Soros had been funding anti-government groups.

"Anyone who is in cahoots with Soros to topple the government should be regarded as a traitor even if the individual once contributed to the country," she said, in a clear reference to Dr Mahathir, who stepped down from the Umno presidency in 2003.

Dr Mahathir, 91, has formed a new opposition party, attracting several former Umno leaders and members in his effort to oust Mr Najib, who is also Umno's president.

The open criticisms come amid expectations that a general election may be called next year instead of in 2018.

Tun Dr Mahathir continued to retain respect in Umno as many appreciate his leadership in raising Malaysia from a low-income commodities exporter to one of the more successful developing nations.

The attacks against Dr Mahathir at this year's five-day assembly beginning on Tuesday is in stark contrast to last year's meeting, when party leaders kept mostly mum despite continuous criticisms hurled by the former leader against Mr Najib over the financial scandal involving state fund 1Malaysia Development Berhad.

"For 22 years, he was our leader. We praised, revered and supported him. Look at what happened," Tan Sri Shahrizat said.

Said Youth chief Khairy Jamaluddin to loud cheers: "We will always remember your contributions, Tun. However, we shall fight your betrayal and desertion till the end."