Lebanon's Iran-backed Hezbollah movement on Friday said it would be "fully prepared" to join its ally Hamas in the war against Israel when the time is right.

Hezbollah deputy chief Naim Qassem spoke as Hamas and Israel traded heavy fire for a seventh day, after hundreds of Hamas gunmen stormed across the border from Gaza into Israel on Saturday and killed more than 1,300 people.

Israel has retaliated by raining air and artillery strikes on Hamas targets in the Gaza Strip, killing at least 1,537 people.

"We, as Hezbollah, are contributing to the confrontation and will (continue) to contribute to it within our vision and plan," Qassem told a pro-Palestinian rally in Beirut's southern suburbs.

"We are fully prepared, and when the time comes for action, we will take it," he said.

The official, whose remarks coincided with a visit by Iran's foreign minister to Beirut, rebuffed calls for Hezbollah to stay out of the war.

An outreach by "major countries, Arab countries, and envoys from the United Nations, directly and indirectly, asking us not to interfere in the battle, will not affect us", he said, adding that "Hezbollah knows its duties".

Israel has traded fire with Hezbollah and allied Palestinian factions in Lebanon in recent days, although the tit-for-tat attacks have remained limited.

On Monday, Hezbollah said Israeli strikes killed three of its members, while Palestinian fighters claimed a thwarted infiltration bid.

Israel said it hit Hezbollah observation posts on Tuesday, while Hamas's armed wing claimed rocket fire.

On Wednesday, Hezbollah said it targeted an Israeli position near the village of Dhayra. Israeli retaliatory fire shortly after wounded three people and turned Dhayra into a ghost town.