The United Nations (UN) insisted on Tuesday that Israel must not only investigate alleged unlawful killings in Gaza like the hospital strike that killed 20 people, including journalists, the previous day, but also ensure those probes yield results.

"There needs to be justice," UN Human Rights Office spokesman Thameen Al-Kheetan told reporters in Geneva, adding that the large number of media workers killed in the Gaza war "raises many, many questions about the targeting of journalists".

His comments came after an Israeli strike on the Nasser Hospital in the southern Gaza town of Khan Yunis on Monday killed at least 20 people, including five journalists, sparking an international outcry.

Reuters, the Associated Press and Al Jazeera all issued statements mourning their slain contributors, while the Israeli military said it would investigate the incident.

Al-Kheetan said at least 247 Palestinian journalists have been killed since the war began in 2023.

He called for an investigation into whether Monday's attack could amount to a so-called "double-tap" strike, in which an initial strike is followed by a second hitting rescue workers and other civilians.

"We can say that the Israeli military reportedly launched multiple air strikes on the Nasser Medical Complex, and there were two air strikes in a short period of time," said Al-Kheetan.

"We know that one of the five journalists appears to have been killed in the first air strike while three others, including the woman journalist, appear to have been killed in the second air strike," he added, describing this as "a shock" and "unacceptable".

"This incident and the killing of all civilians, including journalists, must be thoroughly and independently investigated, and justice must follow." (AFP)