Eight rockets hit an Iraqi base used by American forces on Sunday evening, injuring four people, soon after the leader of Lebanon’s Iran-backed Hezbollah militia warned the United States it faced a prolonged campaign to end its presence in the Middle East for killing a top Iranian general. The Iraqi military said the attack with Katyusha-type rockets wounded two Iraqi officers and two airmen at Balad air base, 80 kilometres north of Baghdad. The attack came days after Iran fired a barrage of missiles at two other Iraqi bases used by US forces in retaliation for the killing of Qassem Suleimani in Baghdad on January 3. There were no casualties from the missile strikes, after which Iraqi and US leaders sought to downplay the prospect of an outright conflict. But Hezbollah leader Hassan Nasrallah suggested on Sunday that it was only the start of a campaign against American forces in the region. “What happened ... is a merely a slap in the face of America,” Nasrallah said in a speech to mark a week since the death of Suleimani in a US drone strike that also killed Iraqi militia leader Abu Mahdi Al Muhandis. “The response to Suleimani’s death is not a single operation but a long path that must remove US military presence from the region,” he said. The killing triggered anger among Iranians but that sentiment turned against the Iranian government and military on Saturday when, after days of denial, they admitted mistakenly shooting down a passenger plane leaving Tehran airport on Wednesday. All 176 people aboard the Ukraine International Airlines flight 752 died, including 82 Iranians. The plane was shot down early on Wednesday, hours after Iran launched the missile attack on US military bases, and Iranian officials said they had been on high alert for a US response. As thousands of people took to the streets across Iran, US President Donald Trump warned Tehran that the world was watching its response after a bloody crackdown on protests on November. Protesters in Tehran chanted “Death to Khamenei” in reference to the country’s all-powerful supreme leader and demanded the resignation of top officials. “Commander-in-chief resign, resign,” hundreds of people chanted in front of Tehran’s Amirkabir University in footage shared online. Other online videos showed protesters cheering as they tore down banners of Suleimani and Mr Khamenei, and chanting “Revolutionary Guard, you are the same as ISIS”. Protests spread from Tehran to Shiraz, Esfahan, Hamedan and Orumiyeh. More videos posted online on Sunday showed protesters shouting anti-government slogans and gathering near Tehran’s Azadi Square despite a heavy police presence. Other videos suggested similar protests were taking place in other Iranian cities. A leader of Iran’s opposition Green Movement, Mehdi Karroubi, called on Supreme Leader Ali Khamenei, the top authority in the Islamic Republic, to step down over the handling of the shooting down of the Ukrainian airliner. In a statement posted online, Mr Karroubi asked when Mr Khamenei was told about the shooting down of the plane after it took off from Tehran and why there had been a delay in informing the public about the real reasons for the crash. Meanwhile, Britain’s Foreign Office confirmed late on Saturday that the country’s ambassador in Tehran had been briefly detained by Iranian authorities. Tehran’s Tasnim news agency said the envoy was arrested for several hours in front of Amirkabir University for inciting anti-government protesters. “The arrest of our Ambassador in Tehran without grounds or explanation is a flagrant violation of international law,” Foreign Secretary Dominic Raab said in a statement. “The Iranian government is at a crossroads moment. It can continue its march towards pariah status with all the political and economic isolation that entails, or take steps to de-escalate tensions and engage in a diplomatic path forwards,” Mr Raab said. Mr Raab and German Chancellor Angela Merkel on Sunday issued a statement reaffirming their commitment to the 2015 nuclear deal between Iran and world powers that lifted international sanctions on Tehran. Mr Trump pulled the US out of the “flawed” deal in 2018 and reimposed sanctions on Iran to force a renegotiated agreement that includes curbs on Tehran’s missile development and regional interference. Mr Trump, who has said he does not seek “regime change” in Iran, took to Twitter to express his support for the Iranian demonstrators, writing: “We are following your protests closely, and are inspired by your courage.” “The government of Iran must allow human rights groups to monitor and report facts from the ground on the ongoing protests by the Iranian people. There can not be another massacre of peaceful protesters, nor an internet shutdown. The world is watching,” Mr Trump wrote. Despite denials, Iran now faces accusations of attempting to cover up the incident. Debris from the crash site was being cleared soon after the Wednesday’s downing and Tehran refused to hand over the black boxes to international investigators saying that their own analysis would tack several months and the full investigation would last up to a year. Crash investigation experts sounded the alarm that the removal of debris and the fact the site was not cordoned off to the public risked contaminating the evidence and leaving experts unable to fully ascertain the causes of the crash. Ukraine’s President Volodymyr Zelenskiy said on Saturday that the findings by Ukrainian experts in Iran meant that the truth about the crash of a Ukrainian passenger plane could not be concealed. “The Islamic Republic of Iran deeply regrets this disastrous mistake,” President Hassan Rouhani wrote on Twitter, promising that those responsible would be prosecuted. “My thoughts and prayers go to all the mourning families.” The Revolutionary Guard, in a rare step, apologised to the nation and accepted full responsibility. The aerospace commander of the Revolutionary Guard, Brig Gen Amirali Hajizadeh, said he had informed Iran’s authorities on Wednesday about the unintentional strike, a comment that raised questions about why officials had publicly denied it for so long. Iranian Foreign Minister Javad Zarif wrote on Twitter that “human error at [the] time of crisis caused by US adventurism led to disaster”, citing an initial armed forces investigation into the crash. The US said its killing of Suleimani, who oversaw Iranian proxy forces in the region, was based on evidence he was planning attacks on American embassies and troops. It was carried out two days after the US embassy in Baghdad was besieged by fighters and supporters of Iran-backed Iraqi militias in response to US air strikes on the Kataib Hezbollah group headed by Muhandis. Those strikes in turn were prompted by the death of a US civilian contractor in one of a series of unclaimed rocket attacks on American targets in Iraq – part of pattern of escalation set in motion by Mr Trump’s decision to withdraw the US from the nuclear deal with Iran in May 2018 and impose tough sanctions targeting the Iranian economy and particularly its oil exports. The other signatories to the deal – Russia, China, Britain, France and Germany – remain in the pact, which places curbs on Iran's nuclear programme to prevent it from developing an atomic weapon. Iran has been incrementally breaching the deal’s restrictions on nuclear enrichment and stockpiles to pressure France, Britain and Germany to find ways around the US sanctions.