Former Prime Minister Nawaz Sharif returned from exile to an ecstatic welcome from thousands of his supporters, and planned to register his candidacy Monday ahead of the deadline for Pakistan's key January elections. Sharif immediately stepped up the pressure on US-backed military ruler Pervez Musharraf to end emergency rule. The arrival Sunday of one of Musharraf's harshest critics was a fresh challenge for the president, who has faced intense domestic and international condemnation since he declared a state of emergency on Nov. 3, locking up thousands of opponents, purging the Supreme Court and muzzling the media. Sharif, who was ousted by Musharraf in a 1999 coup, threatened to boycott the Jan. 8 vote if Musharraf does not end emergency rule. An opposition boycott could deal a severe blow to the president, who has claimed Pakistan is heading toward democracy. "Musharraf has taken this country to the brink of destruction," Sharif told crowds of supporters and onlookers from the top of a truck carrying him from the airport into his home city of Lahore. "When the constitution, fundamental rights are suspended, when people live difficult lives, when judges who make decisions according to the constitution are ousted, will elections in such a situation not be a fraud?" he said. "Should not such elections be boycotted?" Sharif asked, prompting chants of "boycott, boycott!" He arrived from Saudi Arabia, where has spent most of his eight years in exile. Musharraf swiftly booted Sharif back to the kingdom when he flew into Pakistan in September. But the Pakistani leader appears to have lost the support of the Saudi royal family, who provided a special flight to carry Sharif and a host of his relatives home. Sharif had to fight his way through wildly cheering supporters outside the airport terminal. He looked composed as he insisted that his return was "not the result of any deal" with Musharraf. A car carrying Sharif left the airport in a snail-paced procession toward a shrine in the center of the city, surrounded by supporters waving the green flags of his party and chanting "Musharraf go!" Police had deployed some 5,000 officers to prevent chaos at the airport and protect Sharif from the fate of former Prime Minister Benazir Bhutto, whose homecoming was wrecked by a suicide bombing that killed about 150 people. Sharif's party has said he and his brother will file their papers before Monday's deadline for nominations for the Jan. 8 vote. Bhutto filed her nomination papers on Sunday, but both former premiers say a broad opposition coalition could still decide to boycott if Musharraf does not take steps to ensure the election is fair. Equally tricky for Musharraf would be an alliance between Sharif and Bhutto. Washington had been coaxing Bhutto toward an alliance with the embattled dictator until the emergency threw Pakistani politics into confusion. Bhutto welcomed Sharif's surprise return and did not rule out an election alliance with her former political foe. Musharraf is moving quickly to ease some of the restrictions he imposed under the emergency and to belatedly make good on a pledge to end military rule. He is expected to step down as army chief within days and take a new oath as a civilian head of state. Most of the thousands of opponents, human rights activists and lawyers detained since Nov. 3 have been released. But Musharraf has so far resisted strong pressure from the United States - his biggest foreign ally - to lift the emergency and restore the constitution.