"No country and no nation stand to gain from a further escalation in the Middle East," an EU spokesperson said after Ismail Haniyeh was killed.
The European Union has called for "maximum restraint" in the aftermath of the assassination of Ismail Haniyeh, the political leader of Hamas, a development the international community fears could inflame tensions in the already-fraught region and eradicate any fragile hopes of achieving a ceasefire in the Gaza war.
"We call on all parties to exert maximum restraint and avoid any further escalation," said Peter Stano, the European Commission's spokesperson for foreign affairs.
"No country and no nation stand to gain from a further escalation in the Middle East."
Haniyeh was killed on Wednesday in a predawn airstrike in Teheran, where he had travelled to attend the inauguration of Iran's new president, Masoud Pezeshkian. Hamas immediately blamed Israel for the attack and declared Haniyeh a "martyr."
The Hamas armed wing, the Al-Qassam Brigades, said the assassination "takes the battle to new dimensions and will have major repercussions on the entire region" and that Israel "made a miscalculation by expanding the circle of aggression."
Meanwhile, Iran's Supreme Leader has vowed a "hard punishment" for Israel. "We consider his revenge as our duty," Ayatollah Ali Khamenei said.
The Israeli government has not commented on the assassination.
Nearby countries, such as Qatar, Turkey, Jordan and Oman, have condemned the operation, warning it would imperil the months-long mediation efforts to secure a ceasefire. China and Russia, two allies of Iran, have also spoken up in critical terms.
The White House said it did not have any prior knowledge of the airstrike and joined the chorus of voices urging for de-escalation.
"The EU has a principled position of rejecting extrajudicial killings and of supporting the rule of law, including in international criminal justice," Stano said in his statement provided to Euronews, noting the prosecutor of the International Criminal Court (ICC) had sought an arrest warrant against Haniyeh for various charges of war crimes.
The attack has put the international community on edge, as it comes amid a spike of tensions in the low-level war between Israel and Hezbollah, the Lebanese militia.
In the hours before Haniyev's assassination, the Israeli military had struck Beirut, targeting a senior Hezbollah commander in retaliation for Saturday's killing of 12 people in the Israeli-occupied Golan Heights. (Hezbollah has denied any responsibility.)
The rapid succession of events has fuelled fears of a wider, unpredictable military confrontation involving several regional actors, including Iran.
It has also cast serious doubts over the three-phase deal that US President Joe Biden has proposed to end the war in Gaza, which has served as the basis for negotiations between Israel and Hamas. Haniyev, who had lived mostly in Qatar since leaving Gaza in 2019, was considered a key figure in the talks – even if Israel had several times blamed him for refusing to release the hostages still alive in captivity.
Earlier on Wednesday, Josep Borrell, the EU's foreign policy chief, said: "We have to ask for ways to de-escalate tensions and avoid the war which would have an impact on the whole region and beyond. And we need a ceasefire in Gaza now."