European officials have warned citizens that "vigilance is the order of the day" amid fears Iran could activate terrorist sleeper cells to spark chaos across the continent

Fears are mounting that Iran can strike targets inside Europe amid warnings sleeper cells across the continent could be activated to unleash chaos.

What remains of Tehran's leadership has frantically fired missiles and drones at American allies after Donald Trump and his Israeli counterpart approved devastating air strikes on Iran on Saturday morning. The barrage wiped out Iran's leadership, including killing the country's Supreme Leader Ayatollah Ali Khamenei.

Iran responded by firing missiles and drones at Arab states, Israel and even the island of Cyprus, home to British air bases. Among Iran's arsenal include the Khorramshahr 4 missile. The missile has a range 1,242 miles to 1,864 miles and can carry a devastating warhead.

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The missiles could reach as far as Rome, Copenhagen, Budapest and Athens. Dr Sidharth Kaushal, a senior research fellow at Royal United Services Institute told The Daily Mail the missile was a "derivative" of ones used by North Korea.

"It was always speculated that this would have been the delivery vehicle for a nuclear warhead if the Iranians had ever developed one," he said. The Khorramshahr 4 missile can be launched in volleys and, if used, could reach large areas of Europe including Greece, Italy, Germany, Poland and Denmark.

Trump boasted last year Iran's nuclear weapons programme had been "obliterated" but raised fears the country could develop a weapon of mass destruction if left alone. Shahed suicide drones, with a range of 1,242 miles, could also reach parts of Europe - with an array of missiles with shorter ranges already reaching countries across the Middle East including Israel, the UAE and Bahrain.

Though the drones are slower than missiles, they are easier to launch in large numbers and could heap pressure onto target countries if they are used in repeated waves to wear down air defences. Dr Kaushal warned that as the US and Israel continue to batter Iran's senior defence leadership, the country's 'mosaic warfare' doctrine could make it more difficult to predict next moves.

"Ever since the 2000s, the Iranian concept of so-called 'mosaic warfare' [has been] built around the idea that their leadership might be crippled in a war with the United States, and so they would have to devolve control down the levels of command to ensure that their military could continue to function," he said. "The basic concept is that people at lower levels [who] may have been given standard... rules of engagement in peacetime would presume greater authority if they can't make contact with higher command. There is a question of just how much authority to do things that might widen the war sits now with people who would not have [ordinarily] controlled."

The joint US-Israeli air strikes have also raised fears Iran could use sleeper terror cells to attack targets across Europe. A sleeper cell typically infiltrates a country and hides in plain sight until they are activated to carry out terrorist attacks.

Marc Henrichmann, a member of the German parliament's intelligence committee, yesterday warned the attacks would not remain confined to the Middle East. Speaking to local outlets, he added: "The escalation in the Middle East doesn't just affect the region itself.

"The Iranian regime has repeatedly demonstrated in the past that it carried out its terror beyond its own borders. Iranian sleeper cells in Europe cannot be ruled out' as a part of Tehran's retaliation strategy. Vigilance is the order of the day."

The war with Iran appears to be unpopular with many Americans with only one in four agreeing with Trump's decision to strikes. In contrast 43 per cent disapproved and 29 per cent said they were not sure, according to a Reuters/Ipsos poll.