Pakistan's government on Saturday rejected a ultimatum for Prime Minister Imran Khan to step down as the military warned tens of thousands of opposition protesters gathered in the capital that they would not be allowed to “create instability”. About 30,000 protesters led by the hardline Islamist Jamiat Ulema-e-Islam (JUI-F) party descended on Islamabad late on Thursday in a show of political force to demand the removal of the prime minister. Maulana Fazlur Rehman, the JUI-F chief, told the Azadi March gathering on the city's outskirts on Friday night that Mr Khan had two days to resign. “We will not be able to exercise any patience after that point,” he said. But the demand was rejected as “out of the question” after Mr Khan's negotiation team held a day of meetings on how to deal with the stand-off. Mr Rehman, a one-time Islamist firebrand who is seen as a wily political opportunist, alleges last year's general election was rigged and hopes to capitalise on public dismay at rising prices and an economic slump. He asked “state institutions”, a term widely used to mean the country's powerful military, to stop supporting the “illegitimate government”. Opposition leaders claim Mr Khan won with backing from a military which has ruled Pakistan directly, or pulled strings behind the scenes, for much of its history. The military denies meddling in democracy. Major General Asif Ghafoor, director general of the military's information wing, said Mr Rehman should “clarify which institution he is talking about”. “Pakistan’s armed forces are an impartial state institution which always supports democratically elected governments,” he said. “Nobody would be allowed to create instability as the country cannot afford chaos.” Pervez Khattak, the defence minister, told a press conference on Saturday afternoon that there would be no discussion of the prime minister stepping down. The protest is seen as the biggest political challenge of Mr Khan's premiership and also the first significant test of opposition strength during his tenure. Mr Rehman's party has little political clout, but is seen as a potent grass-roots mobiliser through its network of religious schools and seminaries. Bigger opposition parties have lent their support, although they appeared to be hedging their bets to see what happens. Bilawal Bhutto-Zardari, leader of the Pakistan Peoples Party, and Shehbaz Sharif, president of the Pakistan Muslim League, both addressed the gathering. Major arteries in the city remained sealed by shipping container barricades, amid fears the protesters would break their agreement with the police and move into the capital's “red zone” housing embassies, ministries and the parliament. Mr Khan, a former cricketer, rose to power in July 2018 on a campaign to sweep away the country's corrupt, dynastic political elite. He has since been fighting an economic slump and balance of payments deficit that have pushed up prices and unemployment. The economic crisis has taken the shine off his campaign promises for many voters, but his support base has been pleased to see several opposition leaders detained in an anti-corruption purge. The opposition says the prosecutions are politically motivated. The protesters in Islamabad, who appeared to be mainly from the JUI-F heartlands in Khyber Pakhtunkhwa and Balochistan, told <em>The National</em> they were prepared to stay there as long as needed. “We are here to protest against the government. It's taking our very space to breathe with this economic crisis," said Azim Jan, a 63-year-old retired teacher from Quetta. "God willing, it will go. I will stay until the end.” Mohibullah Khan, a JUI-F party worker from Balochistan, said: “We want to get rid of this new system, because there was no fair election. [Khan] came on the back of the army and the establishment. We will spend three days here and after that we will move to the centre of the city.”