Pakistan's fragile coalition split on Monday with Nawaz Sharif-led Pakistan Muslim League (N) withdrawing support to the PPP-led government accusing it of reneging on the promise to reinstate sacked judges.
"The promises made to us were not honoured by the PPP," Sharif, a former Pakistan Prime Minister 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 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.