ISLAMABAD (Reuters) - Pakistan’s former prime minister Nawaz Sharif stepped up his attack on President Pervez Musharraf on Saturday, suggesting he could be hanged while addressing thousands of protesters outside the presidency.

Former Pakistan prime minister Nawaz Sharif waves as he arrives to address lawyers and his supporters during a cross-country rally by lawyers and political activists in Islamabad June 14, 2008. Several thousand protesters gathered outside Pakistan's parliament on Friday for the climax of a cross-country rally by lawyers and activists demanding the reinstatement of judges fired by President Pervez Musharraf. REUTERS/Faisal Mahmood

“We asked you to quit with honor after the election but you didn’t,” Sharif told the crowd, referring to U.S. ally Musharraf, who overthrew him in a 1999 coup.

“Now people have given a new judgment for you ... they want you to be held accountable,” he said in the early hours of Saturday.

The crowd, officially estimated at up to 20,000, chanted “hang Musharraf” as it listened to the two time former prime minister’s fiery speech.

“Is hanging only for politicians?” asked Sharif, referring to former prime minister Zulfikar Ali Bhutto, hanged by a military dictator in 1979.

“These blood-sucking dictators must be held accountable.”

The demonstration, a few hundred meters from the presidency and parliament buildings, marked the climax of an almost week-long rolling protest across the country led by lawyers, though by the end they were easily outnumbered by Sharif party activists.

The United States and other Western allies fear prolonged political instability in the turbulent nuclear-armed Muslim nation will play into the hands of Islamist militants and undermine the U.S.-led campaign against terrorism.

Sharif has called for Musharraf to be tried for treason for tearing up the constitution during a brief spell of emergency rule late last year and for the coup nearly nine years ago.

Helped by Saudi Arabia, Sharif was allowed back from exile late last year as Musharraf’s grip on power slipped following a clash with the judiciary.

His party came second in an election in February that resulted in defeat for pro-Musharraf parties, and brought to power a coalition government led by the Pakistan People’s Party of assassinated former prime minister Benazir Bhutto.

PROBLEM FOR MUSHARRAF AND PPP

Asif Ali Zardari, Bhutto’s widower and political successor, is trying to take away Musharraf’s powers through changes to the constitution that will take months to pass, and the PPP is worried that Sharif is making more political capital by seeking Musharraf’s humiliation.

Sharif was barred from contesting the election, but he will contest a by-election on June 26 for a National Assembly seat.

Treading a careful line, Zardari congratulated the lawyers on their “long march”, a cross-country convoy of cars that set off days ago for the capital.

Security was tight as the rally ended just as dawn broke on Saturday. An avenue in front of the parliament building was sealed off but there was no violence.

Lawyers mingled with flag-waving supporters of Sharif’s party, conservative religious activists, rights workers and students on a wide road overlooking the National Assembly.

Unlike the beatings and tear-gas that protesting lawyers got from police under a pro-Musharraf government last year, the new government ordered police to assist this week’s protest.

“This unprecedented gathering in Islamabad shows the flourishing of democracy under the government of Pakistan People’s Party,” Zardari said in a statement.

Musharraf’s problems erupted in March last year when he tried to dismiss the Supreme Court chief justice, Iftikhar Chaudhry.

In November, General Musharraf resorted to emergency rule to purge the judiciary, including Chaudhry, to stop the Supreme Court ruling on whether his re-election while still army chief the previous month was legal.

Having secured the presidency, Musharraf quit as army chief and ended emergency rule in mid-December, but his actions left him increasingly isolated and unpopular.

Political parties backing the lawyers’ movement hope that reinstating the judges will lead to Musharraf’s ouster.