Pakistan's fragile coalition split on Monday with Nawaz Sharif-led Pakistan Muslim League-N withdrawing support to the Pakistan People's Party-led government, accusing it of reneging on the promise to reinstate sacked judges.

"The promises made to us were not honoured by the PPP," PML-N chief Nawaz Sharif told a packed press conference.

The six-month-old coalition has been tethering on the brink of collapse following sharp differences between Sharif and PPP co-chairman Asif Ali Zardari on the issue of reinstatement of judges sacked by the then President Pervez Musharraf [Images] in March last year.

"The PPP has forced us to withdraw support and sit in the opposition," the 59-year-old leader said.

However, he said PML-N will act as a 'constructive opposition' and will continue efforts to bring genuine democracy in Pakistan.

PML-N also announced the candidature of former Pakistan Chief Justice Saeed-uz Zaman Siddiqui for Presidential elections on September six.