Three Gazans were killed and 30 injured by Israeli shelling on Saturday after militants fired an anti-tank rocket at an Israeli jeep, wounding four soldiers, sources on both sides said.

The flare-up was one of the most serious clashes in a single day since Israel's devastating 22-day operation in the Gaza Strip over New Year 2009.

Police in the Gaza Strip on Monday captured a crocodile that roamed the sewerage system of a town in the north of the enclave, the Palestinian territory's Hamas rulers said.

"The Palestinian police were able to use a boat to catch a crocodile that was hiding in the sewerage system in the town of Beit Lahiya in the northern Gaza Strip," the Hamas interior ministry said in a statement.

Three Israeli soldiers were injured on Tuesday morning by an explosion along the border between Israel and the Gaza Strip, the Israeli military said.

"An IDF soldier was moderately wounded and two others lightly wounded while on a routine activity earlier this morning, adjacent to the security fence in the southern Gaza Strip," the military said in a statement.

A Palestinian man apparently suffering psychiatric problems was killed by Israeli troops after he approached Gaza's border fence, Palestinian medical sources said on Monday.

The 20-year-old man, named as Ahmed al-Nabaheen, was injured on Sunday evening, but the Israeli army refused to allow Palestinian ambulances to the scene to transport him, the medics said.

A Palestinian was seriously wounded by cross-border fire from an Israeli tank in the central Gaza Strip on Friday, a spokesman for the Hamas-run health ministry said.

He did not give the man's name or the exact circumstances but said he was 22 years old and close to the border fence with Israel, east of Bureij refugee camp, when he was hit.

Gaza fighters on Monday fired 18 rockets at southern Israel, ending several days of calm, with the armed wing of the ruling Hamas movement saying it was revenge after an air raid killed one of their men.

It was the second straight day in which fighters had fired rockets at Israel in a confrontation which began early on Sunday, and effectively ended three days of calm after an Egyptian-brokered truce went into force at midnight on Wednesday.

Three rockets fired from the Gaza Strip landed in southern Israel early Sunday without causing any casualties, Israeli police said, hours after an Israeli air strike in the Palestinian territory.

"Two rockets fell in an uninhabited sector of the Eshkol district and another near Beersheba. There were no injuries or damage," police spokesman Micky Rosenfeld told AFP.

The skies over Gaza were quiet early Thursday as an Egyptian-brokered truce between Israel and Hamas took hold after a spurt of violence left four Palestinians dead and two Thai workers wounded in Israel.

"There has been no rocket fire at Israel nor any Israeli attacks in the Gaza Strip since Wednesday night," a spokeswoman for the Israeli military told AFP.

Tensions soared around Gaza on Wednesday after Israeli air raids killed four fighters and Palestinian armed groups fired 68 rockets at southern Israel, seriously wounding two people.

It was the biggest surge in cross-border violence since June, and prompted both Israel and Gaza groups to vow they would not allow the attacks to go unanswered.

Doha is increasing its investment in rebuilding Gaza to $400 million, up from $254 million, Gaza's Hamas premier said on Tuesday during a landmark visit by the Qatari emir.

"The emir agreed to increase the Qatari investment from $254 million to $400 million," prime minister Ismail Haniya said during a press conference in Khan Yunis in southern Gaza to mark the emir's visit.