US President Donald Trump left the summit in Canada a day early due to the fast-escalating situation, the White House said on Monday.
French President Emmanuel Macron said Trump had made an offer for a ceasefire between Israel and Iran.
"There is indeed an offer to meet and exchange. An offer was made especially to get a ceasefire and to then kick-start broader discussions," Macron told reporters.
"We have to see now whether the sides will follow."
Trump had earlier urged everyone to immediately evacuate Tehran, and reiterated that Iran should have signed a nuclear deal with the United States.
The air war between Iran and Israel - which began on Friday when Israel attacked Iran with air strikes - has raised alarms in a region that had already been on edge since the start of Israel's military assault on Gaza in October 2023.
"We affirm that Israel has a right to defend itself. We reiterate our support for the security of Israel," G7 leaders said in the statement issued late on Monday.
"Iran is the principal source of regional instability and terror," the statement added and said the G7 was "clear that Iran can never have a nuclear weapon."
Israel attacked Iran on Friday in what it called a preemptive strike to prevent Tehran from developing nuclear weapons. Since then the two Middle Eastern rivals have exchanged blows, with Iranian officials reporting over 220 deaths, mostly civilians, while Israel said 24 civilians were killed.
Iran denies seeking nuclear weapons and has said it has the right to develop nuclear technology for peaceful purposes, including enrichment, as a party to the Nuclear Non-Proliferation Treaty.
Israel, which is not a party to the NPT, is the only country in the Middle East widely believed to have nuclear weapons. Israel does not deny or confirm that.
The United States has so far maintained that it is not involved in the Israeli attacks on Iran although Trump said on Friday the US was aware of Israel's strikes in advance and called them "excellent." Washington has warned Tehran not to attack US interests or personnel in the region.
"We urge that the resolution of the Iranian crisis leads to a broader de-escalation of hostilities in the Middle East, including a ceasefire in Gaza," the G7 statement said, adding the nations were also ready to coordinate on safeguarding stability in energy markets.
An Israeli strike hit Iran's state broadcaster on Monday while Trump said in a social media post that "everyone should immediately evacuate Tehran."
Washington said Trump was still aiming for a nuclear deal with Iran.
Speaking alongside Canadian Prime Minister Mark Carney earlier, Trump said the former Group of Eight had been wrong to kick out Russia in 2014 after it annexed Crimea.
"This was a big mistake," Trump said, adding he believed Russia would not have invaded Ukraine in 2022 had Putin not been ejected.
"Putin speaks to me. He doesn't speak to anybody else ... he's not a happy person about it. I can tell you that he basically doesn't even speak to the people that threw him out, and I agree with him," Trump said.
Though Trump stopped short of saying Russia should be reinstated in the group, his comments had raised doubts about how much Ukrainian President Volodymyr Zelenskiy can achieve when he is schedule to meet the leaders on Tuesday.
European nations had wanted to persuade Trump to back tougher sanctions on Moscow.
Zelenskiy said he had planned to discuss new weapons purchases for Ukraine with Trump.
with Reuters and DPA
