U.S. senators fom both parties are demanding that Secretary of State John Kerry launch an investigation into UNRWA, the United Nations agency delivering aid, food and medical resources to Palestinians living in Gaza and the West Bank. The organization was repeatedly accused by the Israeli Defense Force of hiding rockets for Hamas in its schools. 

Democrat Ben Cardin of Maryland and Republicans Mark Kirk of Illinois and Marco Rubio of Florida, who's often mentioned as a 2016 presidential candidate and is popular with the Tea Party wing of the Republicans, sent a letter to Kerry asking for an investigation into whether the organization played a role in hiding the rockets in its facilities in Gaza.

"Given UNRWA's ties to terrorism in the past, U.S. taxpayers deserve immediate answers and full transparency regarding their intentions and actions. The State Department must make clear to the U.N. that it needs to take all necessary steps to prevent Hamas from using taxpayer-funded property to launch terror attacks against our allies," Sen. Kirk said in a statement.

The letter to Kerry claimed that in September of 2012, almost all of the seats on the organization’s workers union board were “Hamas-affiliated candidates.” 

At least on two occasions, senior administrators at UNRWA said they found rockets in the organization’s facilities and removed them. Spokesmen said they had not been aware of the rockets in the facilities.

The Israeli Defense Force claimed Hamas was firing rockets from UNRWA schools, and in retaliation, launched attacks that hit the schools and killed dozens of civilians seeking shelter there. In total, Israel hit at least six of UNRWA’s schools, according to the organization.

The most recent attack was launched near one of UNRWA’s schools in the southern city of Rafah, which killed 10 people.

U.N. Secretary General Ban Ki-moon called that attack a “moral outrage and criminal act.”

Israel confirmed the attack: "The IDF [army] targeted three PIJ (Islamic Jihad) terrorists on board a motorcycle in the vicinity of an UNRWA school in Rafah," an IDF statement said.

A week earlier UNRWA Spokesman Chris Gunness had said that his organization had reached its “breaking point” after an attack on a UNRWA shelter in northern Gaza. In an interview with Al Jazeera, Gunness broke down in tears when talking about the 20 people who had been killed in the attack in Jabaliya.

At the beginning of the conflict between Israel and Hamas, UNRWA had said they had capacity to serve about 50,000 Palestinians in Gaza. It is now serving over 150,000 people in more than 80 shelters.

According to Senator Kirk's statement, "the United States is the largest single donor to UNRWA and has contributed approximately $5 billion to the organization since 1950. In 2013, the U.S. made a $294 million contribution to UNRWA."