It appears "impossible" for Pakistan to hold a vote on January 8 because of unrest following the killing of Benazir Bhutto, the country's election commission said yesterday.
The announcement could spark protests by parties demanding quick polls to capitalise on sympathy for the slain opposition leader.
The commission said it would announce a new date today after meeting Pakistan's political parties.
Government and election officials earlier said they expect a delay of up to six weeks in the polls, which are seen as key to restoring democracy to the nation as it battles rising attacks by al Qaida and Taliban militants.
Bhutto's party and other opposition groups want the elections on time because they expect large electoral gains amid sympathy for Bhutto and anger at President Pervez Musharraf following her assassination.
Britain and the US are also eager for the vote to take place as scheduled, but have indicated they would accept a slight delay if technical reasons dictated one.
Bhutto's killing last week thrust the country into crisis and triggered deadly nationwide riots, which were especially severe in her home province of Sindh.
"Our offices in 10 districts of Sindh have been burned, the electoral rolls have been burned, the polling schemes, the nomination papers have been burned," commission spokesman Kanwar Dilshad told reporters. "We are in a very tricky situation."
He said it now "looks impossible" to hold the polls on January 8.
Former prime minister Nawaz Sharif, who heads a large opposition party and is a vocal critic of Mr Musharraf, threatened street protests if the vote was delayed. Bhutto's party also wants the vote to go ahead on schedule.
"We will agitate," Mr Sharif said. "We will not accept this postponement."
Bhutto was killed in a gun and suicide bomb attack that the government blamed on Islamic extremists.
Her husband and other opposition leaders have called for an international, independent investigation into the attack and accused President Musharraf of failing to adequately protect her. Some people close to Bhutto have alleged forces close to the US-backed former general may have been involved.
In a statement the government - which has rejected charges of involvement in Ms Bhutto's death - said it was "committed to a thorough and transparent investigation and will not shy away from receiving assistance from outside, if needed."
Meanwhile, US officials said Washington had provided a steady stream of intelligence to Bhutto about threats against her by Islamic extremists after suicide attackers came close to killing her in a massive blast hours after she had returned from self-imposed exile in October.
They also said the US had quietly joined calls for Pakistan to allow international experts to join the investigation into Bhutto's killing. The officials said they expected an announcement soon that investigators from Britain's Scotland Yard would be asked to play a significant role. Any US involvement would be limited and low-key, they said.