Mahathir Mohamad, the former Malaysian prime minister, has quit the country's ruling party.
The influential former leader's resignation from the United Malays National Organisation (Umno) follows a long feud with his successor, Abdullah Ahmad Badawi, the current prime minister.
The move could also deepen cracks that appeared in Umno ranks after the party suffered massive losses in the March general election.
Speaking on Monday, Mahathir said his decision was prompted by a lack of confidence in Abdullah's leadership.
In a speech to some 1,000 people in his home state of Kedah he also urged other Umno members and cabinet members to follow him.
Mahathir appointed Abdullah to succeed him in 2003 after serving as prime minister for 22 years.
But he remained active in politics, wielding significant influence among the party's grass-roots workers.
By late 2004 Mahathir began accusing Abdullah of nepotism, corruption and inefficiency.
Party insiders say Mahathir was angry because many big infrastructure projects he had initiated were cancelled by Abdullah.
Mahathir's decision raises the possibility of large-scale desertions by loyalists, which could split the party and bring down the government.
Umno is the dominant party in the coalition Barisan Nasional administration that has governed Malaysia since independence in 1957.