Internet services have been suspended across Pakistan after violence erupted when the former prime minister, Imran Khan, was arrested at a court appearance in Islamabad and dragged into an armoured vehicle by scores of security forces in riot gear. The arrest of Khan – who was ousted from power last year and has evaded arrest several times since – came hours after he released a video message reiterating his allegations that Pakistan’s powerful military establishment had tried to assassinate him twice. Khan’s arrest is the latest twist in a political and economic crisis that pits the popular former prime minister against the military and the government, led by his successor, Shehbaz Sharif, whom Khan alleges conspired to remove him from power and make threats on his life, charges they deny. Hours after his arrest, protests began to erupt across Pakistan, with the army accused of orchestrating his detention. More than 40 people were arrested and officials said one protester had been killed after they were shot by an officer near a military checkpoint in the city of Quetta. In Karachi, a police vehicle was set on fire and in Lahore, supporters broke into the house of the military corps commander, smashing windows and setting furniture on fire, while shouting: “We warned you not to touch Imran Khan.” Mobile internet services were cut across the country, according to the Pakistan telecommunication authority, and access to Facebook, YouTube and Twitter, where videos of the protests were being widely shared, was restricted. Late on Tuesday the UK Foreign, Commonwealth & Development Office issued a new travel warning advising against travel to several regions of Pakistan, and saying that “further disruption should be expected.” Khan had travelled to Islamabad on Tuesday morning to seek bail in two corruption cases, some of dozens involving corruption, sedition and terrorism that he is facing. As he entered the court premises, Khan was arrested by agents from the National Accountability Bureau, the country’s anti-corruption body, who were followed by a contingent of paramilitary officers. Khan was put into a vehicle with tinted windows and driven off under heavy security, while a scuffle broke out between his supporters and police. According to a statement released by Islamabad police, his detention was connected to a separate case, known as the Al-Qadir Trust case, which involves allegations Khan earned billions of rupees through illegal land transactions and where he had not been granted bail. It stated that Khan would be produced before the court on Wednesday. Khan’s Pakistan Tehreek-e-Insaf party (PTI) called his arrest a “black day for our democracy and country”. Fawad Chaudhry, a PTI spokesperson, alleged Khan had been “abducted from court premises, scores of lawyers and general people have been tortured, Imran Khan has been whisked away by unknown people to an unknown location”. In a video posted to PTI’s official Twitter account, the barrister Gohar Khan alleged Khan had been struck on the head and the legs by paramilitary officers who entered the premises of the Islamabad high court to arrest him. The interior minister, Rana Sanaullah, said Khan’s arrest was because of his failure to turn up to hearings in a corruption case and denied all allegations of torture. “The arrest has been conducted by the National Accountability Bureau for causing losses to the national treasury,” he said. After Khan’s arrest, the chief justice of Islamabad, Justice Aamer Farooq, demanded an explanation “within 15 minutes” from the police chief and the interior ministry secretary as to why Khan had been detained. “Come to court and tell us why Imran has been arrested and in which case,” he said. Farooq said that if they did not appear, he would summon both Khan and the prime minister, Sharif. The arrest warrant for Khan was released soon after, dated 1 May, stating he was accused of “corruption and corrupt practices”. On Tuesday night, the Islamabad high court ruled that the arrest was legal and that Khan had ignored several notices to appear in court. Insp Gen Akbar Nasir Khan, of Islamabad police, urged calm and said the situation in Islamabad was normal. However, in an attempt to prevent protest, a section 144 was imposed in the city to prevent gatherings of more than five people and internet was cut off in some areas. Since Khan fell from power in April last year in a vote of no confidence, he has been on a crusade against Pakistan’s powerful military establishment, and in particular the senior army generals who it is widely acknowledged helped bring him to power. But after the relationship disintegrated, they orchestrated his removal as prime minister. He accused the military and the Sharif government of a “western-backed conspiracy” to topple him and of being behind an attempt on his life in November last year, when a gunman opened fire during a rally in Punjab and Khan was shot in the leg. This week, the media wing of the armed forces issued another strongly worded rebuttal of Khan’s allegations. Yet during this time Khan’s popularity his soared, with many admiring his determination to go up against Pakistan’s military establishment, which has long been Pakistan’s political puppet master. There is widespread discontent with the Sharif government, as inflation and food shortages have rocketed, and it is expected that Khan could return to power in the next general election, due in October, if he is not disqualified from politics before then. Khan has been putting pressure on the Sharif government to call an early general election, claiming that the coalition that took power after he was removed is “illegitimate”.