According to senior members of Hamas and Hezbollah, another Iranian-backed militant group, Iranian security officials helped plan Hamas's surprise attack on Israel on Saturday and approved it at a meeting in Beirut last Monday.
Officers from Iran's Islamic Revolutionary Guard Corps had worked with Hamas since August to plan the land, sea and air incursion, the people said, It was the most serious violation of Israel's borders since the 1973 Yom Kippur War.
They said details of the operation had been refined in several meetings in Beirut between officers of the Islamic Revolutionary Guard Corps and representatives of four Iranian-backed militant groups; The four groups include Hamas, which is in power in Gaza, and Hezbollah, the Shiite militant group and political faction in Lebanon.
U.S. officials say they have seen no evidence of Iranian involvement. "We haven't seen evidence that Iran directed or was behind this attack, but there is certainly a longstanding relationship between the two," U.S. Secretary of State Antony Blinken said in an interview with CNN on Sunday.
Of the meeting, a U.S. official said: "We do not have any information at this time to confirm that."
But a European official and a Syrian government adviser gave the same account of Iran's involvement in the preparations for the attack as senior members of Hamas and Hezbollah.
Asked about the meeting, Mahmoud Mirdawi, a senior Hamas official, said the group was behind the attacks. "This is a Palestinian and Hamas decision," he said.
If Iran was directly involved in the attack, it would bring the country's long-running conflict with Israel into the open, raising the risk of a broader conflict in the Middle East. Senior Israeli security officials have vowed to strike Iranian leaders if they are found responsible for the killing of Israelis.