The U.N. said Tuesday that Israel must not only investigate unlawful killings in Gaza, including a hospital strike that killed 20 people a day earlier, but also ensure those investigations lead to accountability.

"There needs to be justice," United Nations rights office spokesperson 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 Younis 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.

"The Israeli authorities have, in the past, announced investigations in such killings," Kheetan said.