Iran Press/ Asia: Khan and his allies had tried to sidestep a no-confidence motion that seemed certain to unseat him by dissolving parliament.
A five-judge panel unanimously ruled on April 7 that the move breached the country's constitution and ordered parliament to be restored.
Chief Justice Umar Ata Bandial released the quick decision, calling the April 3 ruling by the deputy speaker of Pakistan's National Assembly, the lower house of parliament, unconstitutional.
Before the Supreme Court ruling was announced, security was beefed up at the court, and heavily armed police were deployed outside the building.
After the ruling was announced, opposition supporters in Islamabad's capital raced through the streets, sounding their car horns.
The court also ordered the parliament speaker to hold the next meeting on April 9 to vote on the no-confidence motion. If the opposition wins, there will be a vote for a new prime minister.
Under the law, elections must be held within three months of the dissolution of the National Assembly. But the election commission said in a letter to the president that it would not be possible to hold elections until October.
Opposition leader Shahbaz Sharif, president of the Pakistan Muslim League-Nawaz (PML-N), welcomed the ruling as a victory for "justice and the supremacy of law."
Khan lost his parliamentary majority last week and had faced the no-confidence vote brought forward by a united opposition. But the deputy speaker of the National Assembly, Qasim Suri, a member of Khan's Tehrik-e Insaf party, rejected the motion as unconstitutional, saying it was part of a foreign conspiracy.
Khan has accused the United States of manipulating the opposition because of his warm relations with Russia and China. The U.S. State Department has denied the allegations.
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