The United States has blamed Hamas for the ongoing humanitarian crisis in the Gaza Strip.

Tammy Bruce, a spokesperson for the US State Department, said that all groups in Gaza must follow international humanitarian law. However, she did not confirm if the US would investigate an Israeli military strike that killed 15 people, including paramedics, civil defense workers, and a United Nations official.

When asked about the killings, Bruce told the BBC, “Every single thing that happens in Gaza is happening because of Hamas.”

Her statement comes after a UN humanitarian agency reported that five ambulances, a fire truck, and a UN vehicle were hit one by one in an attack on March 23. The UN said 15 bodies, including paramedics still in uniform, were recovered and buried in a mass grave.

Jonathan Whittall, head of the UN’s humanitarian agency in Gaza, described the scene as horrifying. In a video posted on social media, he said, “Healthcare workers should never be a target.”

In March, Israel resumed its air and ground attacks in Gaza after ceasefire talks with Hamas failed. According to Gaza’s health ministry, which is run by Hamas, more than 1,000 people have been killed since then.