Tens of thousands of anti-government protesters have gathered in Pakistan's capital Islamabad following the arrival of convoys led by a cricket star-turned-politician and a fiery anti-Taliban cleric.



The twin protests led by Imran Khan and the cleric Tahir-ul-Qadri represent the biggest challenge yet to Prime Minister Nawaz Sharif's year-old government.



The two men are demanding the resignation of Sharif who was elected prime minister last year in what they say were fraudulent elections.



Security has been tightened across the capital amid fears of unrest in a country with a long history of chaotic politics and military coups, the Associated Press news agency reported.



The protesters left the eastern city of Lahore on Thursday, vowing to march to the capital and camp out there until their demands for a new government are met.



They remained on the road for two days before entering Islamabad shortly before midnight. Police estimated the crowd at 60,000 people.



Convoy shot at



Earlier in the day, Khan said gun shots were fired at his vehicle as he led an anti-government march to the capital.

Khan was not injured in Friday's attack.

The convoy, which was not bullet-proof, was pelted by a stone-throwing mob, apparently consisting of workers loyal to the ruling Pakistan Muslim League (PML-N) party workers, Khan told Al Jazeera. He said police watched without intervening.

A second convoy by cleric Qadri had taken longer routes in order to avoid some potentially dangerous areas, said Al Jazeera's Asad Hashim, who is covering the protests.

"The journey has been peaceful. We got the word last night at 3am that there was the possibility of attacks at certain places, when we had not reached Gujranwala [...] and we went through those areas quickly," Qadri told Al Jazeera.

"I hope that by the grace of the Almighty, we would be in a position to achieve our goals successfully. But the whole thing will be very peaceful. The government has to resign, and the assemblies have to be dissolved and the new system has to take place."

Pervez Rashid, the federal information minister and a ruling PML-N party leader, said that the attack on Khan's convoy was an unfortunate incident.

"We know that incidents like these lead to conflict between political leaders, and it causes much harm. We are going to try our hardest through our [parliamentarians] and local administration to convince [our local party workers] to approach the situation with patience, even if they are angered," he told a local television news channel.

Television pictures showed local people tearing up posters featuring Khan's party, Pakistan Tehreek-i-Insaf (PTI), and clashing with his supporters.

Concern over stability

Khan and Qadri intend to hold a sit-in until Sharif resigns.

"It is unclear at this point if there will be a combined sit-in when they arrive in Islamabad. Both sides are remaining firm on their demand that the government resign, although the PTI and PAT [Qadri's Pakistan Awami Tehreek movement] differ on what happens after that point," said our correspondent, reporting from the capital.



Authorities had blocked several main roads with shipping containers and barbed wire in the capital in an effort to thwart the marches.

Riot police were out in force but hundreds of protesters began to gather, beating drums, singing and dancing as they prepared to welcome their comrades approaching the city.

"We have come to save our country because of the call of our leader, Imran Khan," said 36-year-old Ajaz Khan in central Islamabad. He was speaking before the shots were fired at Khan.

"We will not leave from here until our leader tells us to go."

The protests have raised questions over stability at a time when the nation of 180 million is fighting an offensive against Pakistani Taliban fighters and the influence of anti-Western and sectarian groups is growing.

In the latest violence, Pakistani police said 10 armed men were killed when security forces thwarted an assault on two air bases near the southwestern city Quetta.

Fighters armed with grenades and automatic weapons attacked the Samungli and Khalid bases on the outskirts of Quetta, the capital of Baluchistan province, late on Thursday night.