Warning sirens sounded before dawn in Israeli communities near the border as the pre-dawn air strikes and shelling prompted Hamas to launch a salvo of six rockets in retaliation.

The Palestinian Islamist group, which has controlled Gaza since 2007, said the rockets were a "direct response to the escalation by the Israeli occupier".

Israel launched a new wave of strikes in reprisal, targeting "additional Hamas military targets" in Gaza, including a "weapons manufacturing site", the military said.

Israel has bombed Gaza almost daily since August 6, in response to the airborne incendiary devices and, less frequently, rockets launched across the border.

The fire bombs, crude devices fitted to balloons, inflated condoms or plastic bags, have triggered more than 400 blazes in southern Israel, according to fire brigade figures.

The fire balloons are widely seen as an attempt by Hamas to improve the terms of an informal truce under which Israel committed to ease its 13-year-old blockade in return for calm on the border.

But so far Israel's response has been to tighten the blockade.

It has banned Gaza fishermen from going to sea and closed its goods crossing with the territory, prompting the closure of Gaza's sole power plant for want of fuel.

An Egyptian delegation has been shuttling between the two sides to try to broker a renewal of the truce.

It was joined this week by Qatar's Gaza envoy Mohammed el-Emadi who delivered the latest tranche of $30 million in aid to the territory on Tuesday before holding talks with Israeli officials in Tel Aviv.

Sources close to the Qatari delegation said the Israelis had told Emadi they were willing to resume fuel deliveries for the power plant and ease their blockade if there was an end to the fire balloons.

Financial aid for the impoverished territory from gas-rich Qatar has been a major component of the latest truce first agreed in November 2018 and renewed several times since.

But Israel also undertook to other measures to alleviate unemployment of more than 50 percent in the territory of some two million people.

Disagreements over their implementation have fuelled repeated flare-ups on the border.

Such flare-ups escalated into major conflicts in 2008, 2012 and 2014, and mediators have been striving to prevent a new war.