KUALA LUMPUR - Malaysia's former prime minister Mahathir Mohamad announced on Monday (Feb 29) his intention to leave the ruling Umno party after months of criticisms of Prime Minister Najib Razak went unheeded.

He told a packed news conference that Umno was no longer what it used to be and is now "Najib's party".

"I want to leave Umno because it is no longer Umno. It is a party dedicated to supporting Najib, protecting Najib to upholding whatever he does, including some of the wrong things he has done", said Tun Dr Mahathir.

"I cannot be a member of such a party," he said, adding that his wife Siti Hasmah Mohamad Ali was also leaving the party.

Dr Mahathir said he will not be joining any other party because he is "Umno at heart".

However, he will be aligning himself to a core group of Malaysians who have the same goal of seeing Datuk Seri Najib removed from power.

This is the second time Dr Mahathir is quitting Umno, which he led from 1981 to 2003 when he was prime minister.

He first quit in May 2008 during the tenure of then Prime Minister Abdullah Ahmad Badawi. In 2009, he rejoined Umno when Mr Najib became prime minister.

The feud between Dr Mahathir and Mr Najib has gripped the nation for almost a year, with Dr Mahathir repeatedly calling on Mr Najib, his former protege, to step down over a financial scandal at state fund 1Malaysia Development Berhad (1MDB).

In a Feb 5 posting on his personal blog, Dr Mahathir wrote that Attorney-General Mohamed Apandi Ali had "no credibility" after he cleared Mr Najib of any criminal offences or corruption arising from a graft probe into a US$681 million (S$959.5 million) deposit in Mr Najib's personal bank account.

Mr Najib replaced the previous attorney-general and appointed Tan Sri Apandi just weeks after a Wall Street Journal report on 1MDB revealed the deposits of vast sums in Mr Najib's accounts.