Islamabad (CNN) -- Supporters of a Muslim cleric who wants Pakistan's leaders thrown out in favor of a caretaker government waited for him to address them in Islamabad on Tuesday after a deadline he set for the current administration to step down expired.
Thousands of people gathered in an area near the parliament building, a regular site of protests in the Pakistani capital. Brief clashes took place with security forces early Tuesday as the crowd moved into the area.
Local media reported that police fired shots in the air and lobbed tear gas at a crowd. The unrest subsided after 10 to 15 minutes, and the crowd continued peacefully.
Thousands of people had assembled in Islamabad on Monday for a nighttime rally at which the cleric, Tahir ul Qadri, called for the dissolution of the existing government. A large number of the supporters who attended the rally remained in central Islamabad Tuesday morning.
Footage from the local broadcaster Ary News showed chaotic scenes of people running and objects being thrown as gunshots echoed in the background. Members of the security forces in body armor were seen carrying guns.
Pakistani authorities and Qadri's supporters offered differing accounts of the moment of unrest, in which no injuries were reported.
Interior Minister Rehman Malik said police were doing their best to protect Qadri and control the crowd. He said the reported clashes are under investigation.
But Qadri's supporters claimed officers had attempted to arrest the cleric only to be prevented from doing so by the mass of people surrounding him.
"Once they realized that the crowd is not letting them come near him, they opened fire in the air unprovoked, which lasted for 10 minutes," said Shahid Mursaleen, the cleric's spokesman.
The crowd then chased the police officers away with sticks, he said, adding that Qadri remained safe and unharmed.
"It's the beginning of the revolution," Qadri said earlier at the nighttime rally. "Dissolve federal and provincial governments by tomorrow morning; otherwise, the public will force them to step down!"
Qadri urged the demonstrators to remain in the capital until they achieve their goals.
"Now and onward, you have to take care of Islamabad," he said. His campaign comes before national elections due this year.
He referred to President Asif Ali Zardari as 'ex-president' and to Prime Minister Raja Pervez Ashraf as 'ex-prime minister.'
But the group's numbers fell far short of what organizers of the "Million Man March" had predicted, with witnesses estimating that some 20,000 people took part.
Malik, who visited rally sites Monday by helicopter, said the turnout numbers showed that Qadri's event had "badly failed."
Many Pakistanis followed the day's events on television as the participants, led by Qadri, headed toward Islamabad with police and soldiers lining the rally route.
Video showed a convoy of buses, vans and cars packed with participants waving the national flag en route to the capital from the large eastern city of Lahore.
Qadri, who traveled in a bulletproof van, has promised a Pakistani equivalent of Egypt's Tahrir Square protests.
When the marchers arrived at the rally site, near Parliament and the presidential home, they joined more than 1,000 other protesters who had arrived earlier in the day for the demonstration.
Return from self-imposed exile
After eight years in Canada, Qadri returned last month to Pakistan, where he is waging a campaign against the political elite.
Qadri has called for a caretaker administration to replace the current government and to carry out election reforms.
His suggestion that the judiciary and the military weigh in on the composition of the interim government has raised concerns in a country where military leaders have repeatedly seized power and ruled for long periods of time.
Some Pakistanis, noting that Qadri served as a lawmaker in the early 2000s, when Gen. Pervez Musharraf was leading the country, have suggested he may be working on behalf of the military.
Qadri denies those allegations and maintains he is simply seeking to ensure a corruption-free electoral process.
The current government and opposition have both rejected his requests for a caretaker administration, insisting that nothing will stand in the way of timely elections and the democratic process.
"We will not succumb to these illegal demands," Malik said last week.
Party withdraws support
The only political party that had supported Qadri's demonstration, the Mutahida Qaumi Movement, withdrew that support last week. The movement is a coalition partner in the current government.
If this year's elections take place without major difficulties, it would represent the first time in Pakistan's history that a civilian government would have made it through a five-year term.
Corruption is widely considered a chronic problem in Pakistan's political system; President Zardari has served prison time on corruption charges.
The problem appears to be regional. Qadri's campaign comes more than a year after anti-corruption demonstrator Anna Hazare roiled Indian politics with a hunger strike that called for the introduction of strong anti-graft measures.
CNN's Aliza Kassin, Saima Mohsin and Nasir Habib contributed to this report.