Members of the Ezzedine al-Qassam Brigades, the armed wing of Hamas MAHMUD HAMS/AFP/Getty Images

The Israeli Security service Shin Bet has accused the Gaza head for the Christian charity World Vision Muhammad Halabi of funneling "tens of millions of dollars" to Hamas in the Gaza strip after he was handpicked by the Palestinian group to infiltrate the US-based NGO.

World Vision and Halabi's lawyer have denied the accusations by Israeli security services which claimed the trained engineer siphoned off the majority of the Christian charity's funds – 60% – into the hands of Hamas.

"Israel can link anyone living in the Gaza Strip to Hamas. Mohammed [Halabi] does not belong to the organisation nor is he affiliated with Hamas," Halabi's lawyer Mohammed Mahmoud told the Israeli newspaper Haaretz.

Mahmoud said Halabi had explained to Shin Bet that armed Hamas members came in two commercial vehicles with a machine gun mounted taking what they wanted – such was the nature of absolute Hamas rule in the Gaza strip.

World Vision has said in a statement that it rejects the accusations against its manager. "Based on the information available to us at this time, we have no reason to believe that the allegations are true. We will carefully review any evidence presented to us and will take appropriate actions based on that evidence," the charity said.

"World Vision programs in Gaza have been subject to regular internal and independent audits, independent evaluations, and a broad range of internal controls aimed at ensuring that assets reach their intended beneficiaries and are used in compliance with applicable laws and donor requirements," it added.

Shin Bet has said in statement, following the lifting of a gag order that had previously stood over the case, that Halabi "controlled the budget, equipment and humanitarian aid packages worth tens of millions of dollars". It said that its investigation had shown "the cynical and crude way in which Hamas takes advantage of funds and resources from international humanitarian aid organisations."

According to the Israeli security service Halabi had commonly offered fake tenders whereby the wining bidder was aware 60% of funds would go to Hamas' military wing.

Halabi was arrest on June 16 when he was taken into custody at the Erez Crossing by the Shin Bet wile travelling back to Israeli from Gaza. His family has said they have been given no indications as to why he was arrested or his charges..

Shin Bet alleged Halabi was able to skim off a sum of $80,000 contributed by British donors to assist Palestinian families, Gaza Strip. This sum it said was used to bolster Hamas' position prior to the 2014 Israel Palestine war and to pay salaries and bonuses to fighters.