Pakistani opposition figures ramped up calls for the fall of Prime Minister Nawaz Sharif's government on Saturday, but failed to attract massive crowds of protesters promised at rallies in the capital.
Addressing protesters he had led from the eastern city of Lahore, cricketer-turned-politician Imran Khan said he would stage a sit-in that would continue until Sharif leaves office, lashing out at the government he claims was elected fraudulently.
Meanwhile populist cleric Tahir-ul-Qadri demanded Sharif's arrest over what he alleged was the murder of his supporters, and called for the installation of an interim national government.
Qadri late Saturday issued a 48-hour ultimatum to government to accept his demands and threatened that he would not be responsible for any repercussions afterwards.
"Nawaz Sharif and Shahbaz Sharif have no right to sit in the government, their cabinets should be dissolved and they should be arrested on murder charges," Qadri said.
Shahbaz is the younger brother of Sharif and chief minister of largest Punjab province.
"The Sharif brothers should step down and fulfil our demands within 48 hours, if they do not do so I will not be responsible for anything," Qadri said, without elaborating on what actions might follow.
Lawyer Mansoor Afridi, who represents Qadri's Pakistan Awami Tehreek (PAT) movement, said a Lahore court had ordered police to investigate the murder claims, but Information Minister Pervez Rashid denied any order was made to arrest Sharif and his brother.
On June 17, at least 10 PAT workers were killed in clashes with police at Qadri's headquarters in Lahore and a judicial commission was formed to probe the killings.
Qadri also called for all four provincial assemblies and Pakistan's national assembly to be dissolved because they were formed in "unconstitutional" manner, in a wide ranging list of demands made on Saturday.
- Words not backed by numbers -
But the fiery rhetoric was not matched by manpower: of the million people promised in Islamabad by Khan and Qadri, just thousands remained in the capital by Saturday evening.
Khan himself spent a portion of the day at his residence in the suburbs of the capital, explaining he had to rest after the long journey while commanding his supporters to stay firmly put on Islamabad's streets.
"We will not go back until all our demands are accepted," Khan said earlier, demanding that all the officials involved in the alleged vote rigging should be tried under the treason law.
Late Saturday Khan also warned Sharif to resign or else his supporters would enter the high security "Red Zone" on Sunday where top government buildings and embassies are located.
The May 2013 general election saw Sharif take power in a landslide, and international observers who monitored the polls said they were free and credible.
The demonstration is the culmination of the "long march" -- in reality a motorised cavalcade -- that set off Thursday from Lahore, situated around 300 kilometres (190 miles) away, to try to topple the government.
Police and witnesses said on Friday that activists from Khan's Pakistan Tehreek-e-Insaaf (PTI) party clashed with supporters of Sharif's Pakistan Muslim League-N (PML-N) in the town of Gujranwala, some 200 kilometres southeast of Islamabad.
The marchers took more than 36 hours to reach the capital as convoys made stopovers in various cities along the road, where they were warmly welcomed by supporters.
Supporters of PTI, which came third in last year's election, lined up to welcome the convoy in towns along the Grand Trunk Road that links Lahore and Islamabad.
Both Khan and Qadri had originally planned for their marches to converge on Islamabad on Thursday, Pakistan's independence day, but they made slow progress.
By Friday evening Khan's march was slowed to a snail's pace by PTI well-wishers.
Security in Islamabad has been ramped up in recent days, with some 30,000 police and security forces on the streets.
The government has agreed to allow the two groups to hold rallies but many of the city's streets are blocked off with shipping containers to protect sensitive areas.
Interior Minister Chaudhry Nisar said that security agencies had issued an alert about two suicide bombers hiding in Islamabad and adjoining Rawalpindi cities.
"There is a grave danger of terrorism and reports of the arrival of two suicide bombers in Rawalpindi and Islamabad, but we are providing security," Khan said.
Government officials have accused march organisers of trying to derail democracy and Sharif said the marches were a distraction from more pressing issues.
Pakistan is waging a military offensive against Taliban hideouts in the northwest, while also trying to boost a sagging economy and solve a chronic power supply crisis.