ISLAMABAD, Pakistan—After months of internal bickering, Pakistan’s governing coalition announced Thursday it will seek to impeach President Pervez Musharraf, cranking up pressure on the U.S.-backed former general to resign.

With his popularity at rock bottom and civilian political forces arrayed against him, the outlook is gloomy for the leader who pushed Pakistan into the U.S.-led war on extremist groups after the Sept. 11 attack on America.

But Musharraf, who is still seen as close to the armed forces he once commanded, appears in no mood to give up without a fight eight years after rising to power in a military coup.

Analysts said the coalition, which swept to power in February elections but has struggled with pressing economic and security problems, is not assured of victory.

Stripping Musharraf of the presidency will require a two-thirds majority of lawmakers voting in a joint session of both houses of Parliament.

Parties in the coalition control 236 of the National Assembly’s 339 seats and as many as 51 of the Senate’s 100 seats. That is at least six seats short, so the coalition will need support from some of the 29 independent lawmakers or defectors from pro-Musharraf parties.

“It won’t be smooth sailing,” said political analyst Mehdi Hasan.

Asif Ali Zardari, leader of the coalition’s biggest party, expressed confidence it will succeed. He called the move to seek impeachment “good news for democracy” in Pakistan.

The decision followed two days of marathon negotiations between Zardari and Nawaz Sharif, who was ousted as prime minister in Musharraf’s 1999 coup and now leads the second-largest party in the coalition.

Their alliance—forged after the February election victory—has been at risk of collapse over differences over how to restore judges fired by Musharraf last year and whether to seek his ouster.