The assassination of Qassem Suleimani may have dealt a devastating blow to hopes of keeping the Iran nuclear deal alive until the US elections next year, European diplomats fear.

There is also concern that the Iraqi parliament will seek to expel the 5,000 US troops based in Iraq, with unpredictable consequences for the region, including the fight against Islamic State.

These private concerns were voiced as European politicians publicly called for all sides to de-escalate the crisis, appeals that are unlikely to be heeded in Tehran, which is intent on some form of reprisal.

The French president, Emmanuel Macron, consulted with his Russian counterpart, Vladimir Putin, by phone and called on Iran to refrain from escalating the crisis. Russia said both leaders agreed the American “action might seriously escalate tensions in the region”.

Reflecting French concerns that the strikes will drive Iraqi public opinion against a continued US troop presence in the country, the foreign minister, Jean-Yves Le Drian, said: “The priority must be to continue the actions of the international coalition against Daesh [Islamic State], which [the coalition] is operating in Iraq at the request of the Iraqi authorities and in support of Iraqi security forces. The coalition’s continuity is essential to preserving the achievements of five years of combat against Daesh and guaranteeing a lasting victory against terrorism throughout the entire region.”

The US secretary of state, Mike Pompeo, said he consulted on Friday with his German, British and Chinese counterparts about the strike, seeking to reassure them that the US was seeking to de-escalate the crisis.

The German foreign minister, Heiko Maas, was the most critical of the European voices, stressing he had told Pompeo that Germany expected US restraint. Maas tweeted: “The US military operation followed a series of dangerous provocations by Iran. However, this action has not made it easier to reduce tensions. I made this point clearly to Pompeo as well.”

The German Green foreign policy spokesman, Omid Nouripour, called for a suspension of all German military operations in Iraq. “Against the background of massive changes in the political environment, the effectiveness of this mission can no longer be demonstrated,” he said.

In a statement that neither condemned nor condoned the killing of Suleimani, the UK foreign secretary, Dominic Raab, said: “We have always recognised the aggressive threat posed by the Iranian Quds force led by Qassem Suleimani. Following his death, we urge all parties to de-escalate. Further conflict is in none of our interests.”

Britain was not consulted about the strike, even though 400 British troops are in Iraq training Iraqi security forces. Equally, the UK was not consulted on Trump’s decision to pull 5,000 troops out of Syria.

The clearest statement of support for Trump’s action came from the Israeli prime minister, Benjamin Netanyahu. “Just as Israel has the right of self-defence, the United States has exactly the same right,” he said.

“Qassem Suleimani is responsible for the death of American citizens and many other innocent people. He was planning more such attacks. President Trump deserves all the credit for acting swiftly, forcefully and decisively.”

Elsewhere in the Middle East, the pro-US Gulf states were cautiously supportive.

But Syria’s President Assad, who received crucial support from Suleimani in pushing back rebel forces, said: “The memory of martyr Suleimani will stay immortal in the consciousness of the Syrian people. They will not forget that he stood by the Syrian Arab Army in defending Syria against terrorism and its supporters.”

Many European capitals will fear that likely Iranian reprisals could deal a near-fatal blow to their efforts to keep the nuclear deal, and wider European relations with Iran, on life support until the possible election next year of a new, more strategic US president willing to keep diplomatic lines open to Tehran.

Profile Who was Qassem Suleimani? Show Hide Qassem Suleimani, killed by a US drone strike in Baghdad, had become well known among Iranians and was sometimes discussed as a future president. Many considered Suleimani to have been the second most powerful person in Iran, behind supreme leader of Iran Ali Khamenei, but arguably ahead of President Hassan Rouhani. He was commander of the Quds Force, the elite, external wing of the Iran’s Islamic Revolutionary Guard Corps, which the Trump administration designated as a terror organisation in April last year. He was born in Rabor, a city in eastern Iran, and forced to travel to a neighbouring city at age 13 and work to pay his father’s debts to the government of the Shah. By the time the monarch fell in 1979, Suleimani was committed to the clerical rule of Ayatollah Ruhollah Khomeini, and joined the Revolutionary Guards, the paramilitary force established to prevent a coup against the newly declared Islamic Republic. Within two years, he was sent to the front to fight in the war against the invading Iraqi army. He quickly distinguished himself, especially for daring reconnaissance missions behind Iraqi lines, and the war also gave him his first contact with foreign militias of the kind he would wield to devastating effect in the decades to come. By the the time the Iraq government fell in 2003, Suleimani was the head of the Quds force and blamed for sponsoring the Shia militias who killed thousands of civilian Iraqis and coalition troops. As fighting raged on Iraq’s streets, Suleimani fought a shadow war with the US for leverage over the new Iraqi leadership. Once described by American commander David Petraeus as ‘a truly evil figure’, Suleimani was instrumental in crushing street protests in Iran in 2009. In recent months outbreaks of popular dissent in Lebanon, Iraq and Iran were again putting pressure on the crescent of influence he had spent the past two decades building. Violent crackdowns on the protests in Baghdad were blamed on militias under his influence.

Eighteen months before his death, Suleimani had issued Donald Trump a public warning, wagging his finger and dressed in olive fatigues. “You will start the war but we will end it.” Michael Safi Photograph: Mehdi Ghasemi/AFP

In the short term, hardliners within Iran are likely to benefit politically from the US airstrike in parliamentary elections this spring. The killing also makes it certain Iran will take its fifth step away from the nuclear deal in the next few days.

Tehran has been staging a phased withdrawal from the agreement in what it says is a response to US sanctions and the European failure to meet commitments to trade with Iran. Plans for the Iranian foreign minister, Javad Zarif, to travel to the US for a meeting of the UN security council in New York are also likely to be jettisoned.

European leaders will be equally concerned that the drone strike might destabilise Iraq further and encourage the Iraqi parliament to go ahead with pre-existing plans to vote to eject all US forces. The prediction by Pompeo, that the killing of Suleimani would lead to “dancing in the streets of Baghdad” is not universally shared.

More predictably, the attacks were condemned by the Russian foreign ministry, a close ally of Iran in Syria, as “a reckless step that is likely to lead to an escalation of tensions in the region”.

China criticised the use of violence in international relations, saying: “The People’s Republic calls on the countries involved – especially the United States – to remain calm and to avoid a further escalation of the situation.”