The United States and European allies called on Iran to "stand down" Monday, as fears mounted of an imminent attack on Israel that could spark an all-out war in the Middle East.

Tensions are soaring in the region, with the United States rushing a missile submarine and an aircraft carrier group in a show of support for its key ally.

Iran and its Lebanese ally Hezbollah have vowed revenge for the killing of the political leader of the Palestinian group Hamas in Tehran, and of a Hezbollah commander in Beirut.

International efforts to stave off an Iranian attack have intensified, with US President Joe Biden and the leaders of France, Germany, Italy and Britain warning Tehran in a joint statement on Monday.

"We called on Iran to stand down its ongoing threats of a military attack against Israel and discussed the serious consequences for regional security should such an attack take place," they said after speaking on Monday.

The White House warned that a "significant set of attacks" by Iran and its proxies was possible as soon as this week, saying that Israel shared the same assessment.

As the frantic diplomacy continued, German Chancellor Olaf Scholz and British Prime Minister Keir Starmer both called on Iranian President Masoud Pezeshkian to de-escalate the situation.

Pezeshkian said Monday his country has the "right to respond to aggressors."

Hamas political chief Ismail Haniyeh had been in Tehran for the new Iranian president's inauguration last month when Haniyeh was killed in an attack that Iran has blamed on Israel.

Israel assassinated Hezbollah commander Fuad Shukr in Beirut a day earlier, leaving the region on edge. 

'No further time to lose'

Israeli military spokesman Daniel Hagari said his country was "ready to foil any threat in real time" but added that he was "not familiar" with reports that Iran was expected to launch an attack in the next 24 hours.

Israel's Defense Minister Yoav Gallant said the country had strengthened defenses and organized "offensive options" as "threats from Tehran and Beirut may materialize."

In a call with the Iraqi prime minister, US Secretary of State Antony Blinken on Monday "reiterated the importance of Iraq's responsibility to protect Coalition military advisors from attacks by Iran-aligned militias" following a recent attack, according to a statement.

Washington and the four European nations have also intensified their calls for a ceasefire in Gaza, regarding the conflict sparked by Hamas's October 7 attack on Israel as the root cause of the tensions in the Middle East.

They backed a call by Biden and the leaders of Egypt and Qatar for renewed talks between Israel and Hamas this Thursday, "and stressed there is no further time to lose." 

They also called for "unfettered" delivery of aid to devastated Gaza.

The pressure to bring an end to the fighting in the Gaza Strip and for Hamas to release its hostages came as the militant group's armed wing said it had killed one Israeli captive and wounded two more in "incidents."

The Ezzedine Al-Qassam Brigades said in a statement that two of its fighters "assigned to guard" the hostages had fired at them in "two separate incidents" and that a committee had been formed to investigate.

Hamas has urged mediators to implement a truce plan earlier presented by Biden instead of holding more talks.

Israel has accepted the latest invitation from the United States, Qatar and Egypt to send negotiators.

"The reason we're doing that is to finalize the details of the implementation of the framework agreement," Israeli government spokesman David Mencer told a news conference.

'Stop this war'

Pressure for a ceasefire in Gaza grew after civil defense rescuers in the Hamas-run territory said an Israeli air strike on Saturday killed 93 people at a school housing displaced Palestinians.

Israel said it targeted militants operating out of the school and mosque.

On Monday, witnesses told AFP Israel struck Khan Yunis and Rafah from the air. Palestinian group Islamic Jihad, which has been fighting alongside Hamas in Gaza, said its fighters were battling Israeli troops in Khan Yunis.

In central Gaza's Nuseirat refugee camp, Suhail Abu Batihan said the Israeli bombardment was "causing terror" among residents, calling on mediators and "the world... to intervene to stop this war."

The Gaza war began with Hamas's October 7 attack on southern Israel which resulted in the deaths of 1,198 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Militants also seized 251 people, 111 of whom are still held captive in Gaza, including 39 the military says are dead.

Israel's retaliatory military offensive in Gaza has killed at least 39,897 people, according to a new toll from the territory's health ministry, which does not provide a breakdown of civilian and militant deaths.

Source: AFP, by Danny Kemp