ISLAMABAD (AP) — Pakistani lawmakers met Wednesday as tens of thousands of protesters thronged outside the assembly calling for the resignation of Prime Minister Nawaz Sharif over alleged voting fraud.

Sharif and other lawmakers were able to enter the building through a back exit connected to the premier's office after the protesters late Tuesday had torn down barricades and entered the so-called Red Zone housing Parliament and other key government buildings.

The twin protests led by the famous cricketer-turned-politician Imran Khan and fiery cleric Tahir-ul-Qadri have virtually shut down Islamabad, raising fears of unrest in the nuclear-armed U.S. ally with a history of military coups and dictatorship.

Despite the mounting pressure, Sharif has refused to step down, while the country's powerful army has called for a negotiated settlement.

"Situation requires patience, wisdom and sagacity from all stakeholders to resolve prevailing impasse," army spokesman Gen. Asim Saleem Bajwa said on Twitter. He said the government buildings in the so-called Red Zone were a "symbol of state" and were being protected by the army.

Khan, the former cricket star leading one of the protests, has called on demonstrators not to enter Parliament but warned he would lead them into the premier's office if Sharif does not step down by Wednesday evening. The premier's office is being guarded by police, paramilitary rangers and troops.

Pakistan Television showed Sharif entering the National Assembly, or lower house of parliament, and meeting with lawmakers from all the major parties except Khan's Pakistan Tehreek-e-Insaf, which is the legislature's third largest bloc.

Lawmakers from several parties condemned the protesters' attempt to besiege Parliament.

"We will foil this conspiracy, and we will defend our democratic institutions," said Maulana Fazlur Rehman, head of the Jamaat-e-Islami party and a Sharif ally.

Shazia Marri, a lawmaker from the opposition Pakistan People's Party, condemned the move to surround Parliament, saying: "We will strive to safeguard democracy. We will strive for the supremacy of the constitution."

Outside the Parliament, Qadri directed his supporters to occupy all the main gates of the building and not to allow Sharif or any other deputies to leave until the prime minister resigns.

"We deliberately gave these lawmakers a chance to enter the Parliament, but now we will not allow any lawmaker to go inside or come out," he said. It was not immediately clear, however, whether the demonstrators would be able to seal off the assembly.

The protesters accuse Sharif of rigging the May 2013 election that brought him to office in the country's first ever democratic transfer of power.

Sharif was forced from office after a previous stint as prime minister in 1999, when the then-army chief Pervez Musharraf seized power in a coup.

A peaceful and celebratory atmosphere prevailed outside the Parliament on Wednesday, with protesters dancing to the beat of drums, singing patriotic songs and chanting against Sharif.

"Yesterday, people were saying we will never be able to reach the Parliament. Look, we are standing right in front of the Parliament," said Rabia Naeem, 22, a Khan supporter. "Imran Khan is the only hope to save Pakistan from corrupt rulers," she said.

Asad Hafeez, a 45-year-old Qadri supporter, said reforms were needed before any new elections.

"We need electoral reforms and a neutral government to hold free and fair elections. It will only happen when Nawaz Sharif resigns," he said.

The U.S. embassy in Islamabad said its consular section would remain closed Wednesday, and advised American citizens to keep a low profile and avoid large gatherings.