ISLAMABAD — Pakistan’s prime minister today tried to keep his government from collapsing after a key party said it was quitting the ruling coalition, leaving the government short of majority support in parliament.

The Muttahida Qaumi Movement, the second largest party in the ruling coalition, said Sunday it would join the opposition because of fuel price hikes, inflation and the ruling Pakistan People’s Party’s general poor performance.

The defection deprives Prime Minister Yousuf Raza Gilani’s government of the 172 seats needed for a majority in the 342-member parliament. That means the fractured opposition parties — if they can work together — could sponsor a no-confidence vote in Gilani, which if passed by a majority of lawmakers would remove the prime minister from office and possibly trigger early elections.

The political crisis could distract the government from its counterterrorism alliance with the U.S., which wants Pakistan to crack down on al-Qaida and Taliban insurgents on its soil, though security is largely the purview of Pakistan’s powerful military.

The turmoil also all but guarantees lawmakers will make no progress anytime soon on solving the economic problems that have frustrated ordinary Pakistanis and forced the country to rely on $11 billion in loans from the International Monetary Fund.