ISLAMABAD, MARCH 30

A main ally of Pakistani Prime Minister Imran Khan quit his ruling coalition on Wednesday after reaching a pact with opposition parties seeking to oust him, signalling Khan may be running out of options as he tries to stay on in power.

Former cricket star Khan, 69, is battling a series of defections from his ruling alliance in the face of increasing questions over his performance, including his government's management of a struggling economy, beset by double-digit inflation and rising deficits.

An increasingly united opposition has moved to force him from office in a no-confidence vote due between Thursday and Monday, in which support from Khan's allied parties was critical.

The leader of Khan's main parliamentary ally, the Muttahida Qaumi Movement (MQM), Khalid Maqbool Siddiqui announced his party was joining the bloc looking to oust Khan following a written agreement between the two sides.

'I announce that we (MQM) are with you (opposition) in this change,' Siddiqui said at a press conference alongside opposition leaders on Wednesday.

Khan's party does not have a simple majority in the National Assembly by itself and needs the support of coalition allies and the MQM, based in the southern port city of Karachi, has been his biggest ally in parliament.

'We have sent our resignations to the prime minister,' Amin-ul-Haq, a member of Khan's cabinet from the Muttahida Qaumi Movement (MQM), told local television channel Geo News.

Khan's ouster would likely mean another round of instability in the nuclear armed south Asian country, in which the military has a long record of intervening in politics and no prime minister has completed a full five-year term in its history.

Opposition parties accuse Khan of mismanaging the economy, foreign policy and resorting to heavy-handed measures against critics.

With the support of the MQM, the combined opposition has, on paper, the requisite numbers to oust Khan when the vote happens in the next five days.

Opposition leaders Shahbaz Sharif and Bilawal Bhutto Zardari, standing alongside MQM's Siddiqui, called on Khan to resign before the vote now that he had lost the majority.

'It is a tradition that if you lose majority, you should step down,' Sharif said.

However, Khan's aides said he will not back down or resign.

'He will not resign. He will fight till last ball,' Interior Minister Sheikh Rasheed Ahmad told reporters after a cabinet meeting on Wednesday. 'He will probably be present in the parliament during the vote on Sunday.'

Ahmad said Khan would also be giving a televised address to the nation later on Wednesday.