Dr Mahathir led Malaysia for more than 20 years
Malaysia's former prime minister, Mahathir Mohamad, has resigned from the ruling party in protest at its poor showing in the general election.
Dr Mahathir said he would not rejoin the United Malay National Organisation until current PM Abdullah Badawi quit.
Dr Mahathir led Malaysia for 22 years and chose Mr Abdullah as his successor, but has since criticised him regularly.
Earlier this year, the ruling coalition suffered its worst election result since independence.
The United Malay National Organisation (Umno) and its partners lost control of five states, as well as their two-thirds majority in the Malaysian parliament.
Dr Mahathir's decision to resign was announced in characteristically dramatic style, according to the BBC correspondent in Malaysia, Robin Brant.
There was no hint it was coming, in the middle of an otherwise normal speech.
In some ways it is unexpected, but when you consider his behaviour over the past few weeks it is not so surprising, our correspondent says.
Mahathir Mohamad has been criticising the Umno-led government and Prime Minister Abdullah almost daily since the party's disastrous result in the election earlier this year.
He was the first high-profile figure to call for the prime minister to quit.
Dr Mahathir led Malaysia through huge economic growth in the 1980s and 90s, and remains an iconic figure who still retains considerable influence.
Announcing his decision to quit, he said: "I will only come back to the party when there is a change in leadership."
He is also urging other senior politicians to follow him, which will only add to uncertainty about how long Mr Abdullah can stay in power.