Pakistan's government on Thursday ordered provincial authorities to ensure tight security for the main opposition leader Nawaz Sharif and his brother when they attend public rallies.
Sharif's Pakistan Muslim League is participating in a "long march" protest by lawyers from Karachi to Islamabad this week to press for reinstatement of judges sacked by former military dictator Pervez Musharraf.
"We have asked all the chief secretaries, home secretaries and provincial police officers to ensure and provide foolproof security to them," interior ministry spokesman Raashid Mazari told AFP.
Asked if the Sharif brothers were in danger, the spokesman said there was no specific threat, but that some "miscreants" could take advantage of the situation.
Interior ministry chief Rehman Malik also told the senate that given the country's current security situation and the "intensive public exposure" of the Sharif brothers "foolproof" security was essential.
Shahbaz Sharif, the former chief minister of Punjab province, responded by accusing the government of plotting against them.
"The letter of the interior ministry is part of a conspiracy hatched against us. There are some forces in the government who want to assassinate Nawaz Sharif," said Rana Sanaullah Khan, the senior leader of Sharif's party.
Khan quoted a letter sent by Shahbaz Sharif in reply to the interior ministry chief.
"I do not care about my life. We can sacrifice thousands of lives for the revival of independent judiciary. We will continue our noble cause", Khan quoted him as saying.
Earlier the Guardian newspaper said Nawaz Sharif, in an interview, accused the government of running an "elected dictatorship" plotting to kill him.
"I have recently received certain information from own sources, credible sources, about certain forces who are active against me," the Guardian quoted him as telling the newspaper from inside an armour-plated Mercedes.
"Threats to my life come from high-ranking government officials, certain topmost people in the government, my sources say," he said.
The Guardian said the former Pakistani premier declined to give further details.
Islamabad denied any plot to kill the main opposition leader.
"There is no such plot of assassination," the interior ministry's Mazari told AFP in response to a question on the media report.
The Sharif brothers have been locked in a fresh political showdown with embattled President Asif Ali Zardari since the Supreme Court on February 25 barred them from contesting elections and holding public office.
Farhatullah Babar, spokesman for President Asif Ali Zardari, dismissed Sharif's reported allegations as a "political gimmick".