GAZA CITY - Israeli warplanes pounded Hamas targets in the Gaza Strip early Wednesday in a new flare-up of hostilities that saw dozens of rockets and mortar shells fired from the Palestinian enclave, the army said.

The strikes targeting Hamas's military wing, the Ezzedine al-Qassam Brigades, were more intense than in previous sorties to convey the message "we will not allow this situation to continue," Israeli military spokesman Jonathan Conricus told reporters.

The latest spike in tensions follows weeks of deadly protests and clashes along the Gaza-Israel border as well as the worst military escalation last month since a 2014 war. It comes as US President Donald Trump's special envoy Jason Greenblatt and adviser Jared Kushner visit the region to discuss issues including the Palestinian-Israeli peace process.

Israeli planes initially targeted three Hamas military positions overnight in Gaza in response to kites and balloons carrying incendiary and explosive devices launched into Israel from the Palestinian territory, the army said. "They may look like toys but I can assure they are not toys, they are weapons intended to kill and to inflict damage," Conricus said. He said that so far Israel had sought to warn off those launching the airborne devices but that could change.

"Hamas and other terrorists, but mainly Hamas" hit back after the first air raids with more than 45 rockets and mortar rounds fired from Gaza towards Israel, seven of which were intercepted by the Iron Dome missile defence system, he added. Three more landed inside the Jewish state, he said, but did not account for the remainder. In response, Israeli planes carried out more raids against 25 "terror objectives" including an underground training compound, according to the army.

Gaza medical sources said that five people were lightly injured in the strikes.

­­Conricus said that most of the 200,000 Israeli civilians who live within range of the short-range rockets fired from Gaza "spent the night in bomb shelters."

Kobi Ivri, a resident of an Israeli kibbutz neighbouring the southern Gaza Strip whose house was damaged by the Gaza fire, said he and his family ran into their bomb shelter after being woken at 5:20 am by a siren.

"There was a boom. I heard glasses breaking, but I understood it (the mortar shell) fell outside, close," he said.

Ivri described "a routine of tension, a routine of anticipation (of attacks), a routine of understanding that not too much is being done in order to help us," noting that an incendiary balloon from Gaza fell at the entrance to his kibbutz on Tuesday.

Early Wednesday afternoon, Israeli aircraft fired near Palestinians in southern Gaza launching incendiary kites, and later in the day, aircraft fired near Palestinians attempting to do the same in northern Gaza, a military spokesman told AFP.

Tensions have soared in Gaza since mass protests and clashes broke out along the border on March 30. At least 132 Palestinians have been killed. There have been no Israeli fatalities.

Palestinians are demanding the right to return to the homes their families fled or were expelled from during the 1948 war surrounding the creation of Israel.

Israel maintains the use of live ammunition is necessary to defend its borders and stop infiltrations.

It accuses Hamas, which controls the Gaza Strip, of seeking to use the protests as cover for attacks.

UN Secretary General Antonio Guterres has warned that Gaza is close to the brink of war.

Israel and Hamas have fought three wars since 2008 and observe a tense ceasefire that is regularly shaken by hostile acts.

Peace talks between Israel and the Palestinians have been stalled since 2014.

On Tuesday Greenblatt and Kushner met with Jordan's King Abdullah II in Amman to discuss the Palestinian-Israeli peace process during a regional tour that will also take them to Israel, Egypt, Qatar and Saudi Arabia.

Trump's controversial December decision to recognise the disputed city of Jerusalem as Israel's capital prompted Palestinians to freeze all contacts with US officials.