At least 15 people, including four journalists working for the international media, are reported to have been killed in an Israeli strike on a hospital in the southern Gaza Strip.

A Reuters cameraman and an Associated Press journalist were among those killed in the attack at Nasser Hospital. Another journalist is reported to have worked for Al Jazeera.

Several people were killed in an initial strike, and others in a second which happened as rescuers attended the scene, the Hamas-run Civil Defence said.

The Israeli military said it had carried out an attack on the hospital and an investigation had been ordered. It added that it “does not target journalists as such”.

In video from the scene, a doctor standing at an entrance to what is the main hospital in southern Gaza holds up bloodied clothes to show journalists following the first strike. Suddenly there is a blast, sending people running for cover as glass shatters. A man injured by the blast is seen trying to drag himself to safety.

In other footage, white and grey smoke can be seen billowing from an upper level of the hospital where damage is apparent. Outside, people are running and shouting amid chaos, as ambulance horns can be heard.

Reuters news agency said its cameraman, Husam al-Masri, was among those killed. The Associated Press (AP) said Mariam Dagga, a freelance journalist working for it, was also killed. AP said it was “shocked and saddened” by the 33-year-old’s death.

The others are said to have been Mohammed Salameh working for Al Jazeera, and photographer Muath Abu Taha. US TV network NBC said Taha did not work for it, as had been initially reported.

The Civil Defence said 15 people were killed, including one of its members, AFP news agency reported.

Monday’s attack comes two weeks after six journalists, including four from Al Jazeera, were killed in an Israeli targeted attack near al-Shifa Hospital in Gaza City.

The UN’s human rights office condemned that attack, calling it a grave breach of international law.

The Israel Defense Forces (IDF) said it had targeted Anas al-Sharif, a prominent Al Jazeera reporter, alleging he had “served as the head of a terrorist cell in Hamas”.

The Committee to Protect Journalists (CPJ), a leading body which promotes press freedom, said Israel had failed to provide evidence to back up its allegations.