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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.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.