Image copyright Reuters Image caption Mahathir Mohamad remains influential in Malaysian politics

Malaysia's long-serving former prime minister, Mahathir Mohamad, has been chosen once again as a candidate to run for the top job, at the age of 92.

On Sunday, he was picked by the opposition alliance as its prime ministerial candidate for a general election that must be called by August.

Mr Mahathir stepped down as prime minister in 2003. He had served in the post for more than two decades.

If he wins, he will become one of the world's oldest leaders.

In recent years, he has been drawn back into politics because of his vocal opposition to current Prime Minister Najib Razak, who has been embroiled in a multi-billion dollar financial scandal involving a state development fund called 1MDB.

Mr Mahathir cut links with the ruling UMNO party and in 2016 started a new party, Bersatu, which joined the Pakatan Harapan opposition alliance.

The former leader's authoritarian but essentially pragmatic policies at home during his tenure helped transform Malaysia into an Asian economic tiger, correspondents say.

However throughout his rule, he took a tough stand against those who opposed him or threatened his power, they add.

His deputy and heir apparent, Anwar Ibrahim, was abruptly sacked in 1998 over political difference, and was then jailed for six years on sodomy and corruption charges.

But the two former political enemies have put aside their differences to take on Najib Razak.

Mr Ibrahim, who led the opposition in the 2013 elections, was again jailed in 2015 on charges he says are politically motivated.

The opposition says that if it wins it will seek a royal pardon for him so he is eligible to be prime minister.