Qatar began distributing millions of dollars in aid in the Gaza Strip on Monday in a fresh bid to restore calm after a flareup with Israel, a Qatari official said.

Gaza's Islamist rulers Hamas, along with an allied terrorist group, Islamic Jihad, fired hundreds of rockets at Israel on May 4 and 5, saying they were frustrated by the slow implementation of a previous ceasefire deal.

Hamas claimed that a new agreement was brokered which reportedly includes tens of millions of Qatari aid to Gaza as part of a package to ease Israel's crippling blockade of the strip.

The Gulf state, a rare Hamas ally in the region, has been providing millions in aid to the strip monthly since November.

Qatari envoy Mohammed al-Emadi entered Gaza early Monday, the Qatari source told AFP on condition of anonymity.

"This morning, the distribution of a cash aid of 100 dollars per poor family began," he said, adding it was destined for 108,000 families.

Hundreds of Gazans waited at post offices in Gaza City to receive the $100 cash payments, an AFP photographer said.

Israel and Hamas have fought three wars since 2008 and analysts fear another round remains likely.

UN envoy Nickolay Mladenov warned Monday of the risk of fresh conflict.

"The risk of war remains imminent and today we have perhaps the last chance to consolidate the agreements that have been reached," he told a press conference in Gaza.

"The next escalation is going to be probably the last."

He said he had seen welcome steps by Israel in the wake of the latest uptick, such as extending the Gaza fishing zone and reopening border crossings.

The UN was preparing a series of projects to improve the lives of people in Gaza, he said.