The family of four Palestinian children killed when Israel bombed a beach during last summer's Gaza war were indignant Friday over the closure of a probe into the incident.

The Israeli army, which launched the investigation after the 50-day July-August war ended, announced late Thursday that the "tragic" attack witnessed by several foreign journalists had not violated international law, and said it was closing the case.

The Israeli army said on Thursday that it was dropping proceedings over a July 16 bombing of a Gaza beach where four children died during last summer's war.

"The... case has been closed following the completion of a criminal investigation," it said in a statement, adding that two other cases involving Palestinian deaths in the fighting had also been closed, but a criminal investigation had been launched in an attack on a cafe in which nine died.

The United Nations on Monday released a "List of Shame" of children's rights violators but did not include Israel, despite an outcry over the death of more than 500 children in the Gaza war.

Rights groups had called on Secretary-General Ban Ki-moon to add Israel to the list and there was much debate among U.N. agencies ahead of the final decision that rested with the U.N. chief.

Israeli warplanes struck Gaza early Sunday for the second time in three days after cross-border rocket fire by an Islamic extremist group which is locked in a power struggle with Hamas.

It was the third time Israel had staged retaliatory air strikes on the war torn Gaza Strip in the past fortnight after three instances of rocket fire, all of which were claimed by Salafist extremists loosely allied with the Islamic State group.

Human Rights Watch on Thursday urged U.N. Secretary General Ban Ki-moon to add Israel to an annual "List of Shame" of children's rights violators, after more than 500 children were killed in the war in Gaza last year.

The U.S.-based rights group called on Ban to resist pressure from Israel and the United States to keep the Israeli Defense Forces off the list due to be released next week.

Israeli warplanes struck militant targets in the Gaza Strip early Thursday after Palestinian rockets hit the Israeli south for the second time in 10 days, sources on both sides said.

Palestinian security sources said the strikes targeted three training bases in Gaza City that were used by Hamas's armed wing, the Ezzedine al-Qassam Brigades, as well as a fourth in the southern city of Khan Yunis.

A Palestinian farmer was wounded on Wednesday after being shot by Israeli troops near the border in southern Gaza, health officials said.

The 22-year-old man was in a moderate condition after being shot in the stomach as he farmed land near the border in an area east of Khan Yunis, Gaza health ministry spokesman Ashraf al-Qudra said.

The impoverished Gaza Strip is a "powder keg" at risk of exploding, German Foreign Minister Frank-Walter Steinmeier said on Monday during a visit to the war-torn territory.

The German minister, who arrived in the region on Saturday and held talks with top Israeli and Palestinian officials, called for efforts to rebuild the shattered enclave which was ravaged by a 50-day war last summer, the third in six years.

The Israeli air force carried out four strikes on militant targets in the Gaza Strip early Wednesday, eyewitnesses said, hours after a cross-border rocket attack on the Jewish state.

The planes targeted training camps belonging to militant group Islamic Jihad in Rafah, Khan Yunis and Gaza City, the witnesses said. There were no immediate reports of casualties.

Amnesty International accused the Islamist movement Hamas Wednesday of committing war crimes against fellow Palestinians to "settle scores" during last year's Gaza war with Israel, executing at least 23 people.

A report by the London-based rights group detailed the "brutal campaign of abductions, torture and unlawful killings against Palestinians accused of 'collaborating' with Israel" by Hamas, de facto ruler of the Gaza Strip enclave.