Switzerland said on Saturday no decision would be taken on an expected aid payment to the UN agency for Palestinian refugees until "serious accusations" against several UNRWA staff were clarified.
The Swiss foreign ministry said it was "extremely worried" about allegations that several UNRWA staff members were involved in Hamas's October 7 attacks inside Israel.
The United Nations agency said on Friday it had fired several employees over the Israeli accusation, which prompted some key donor countries to suspend funding to UNRWA.
The Swiss foreign ministry said the country's annual contribution to UNRWA, around 20 million Swiss francs ($23 million) in recent years, had yet to be approved for 2024.
"No decision will be taken as to this payment until we have more information about the serious accusations against UNRWA staff members," it said.
Switzerland's right-leaning lower house of parliament attempted during general budget discussions last month to strip UNRWA of its annual funding but the upper house opposed the move.
Parliament eventually reached a compromise to cut 10 million francs from the overall humanitarian funding budget, without specifying where the money should be saved.
It said all contributions to humanitarian aid in the Middle East would be paid in instalments and only after consultation with parliamentary foreign policy committees.
"These consultations have yet to take place," the foreign ministry stressed on Saturday.
"Switzerland has zero tolerance for all forms of support for terrorism, and for calls to hatred or incitement to violence," it added.
"(Switzerland) expects that immediate measures will be taken in the face of credible allegations."
It noted that UNRWA had taken immediate measures by firing the accused employees and launching an investigation.
The war in Gaza started after the Hamas attack that killed about 1,140 people in Israel, mostly civilians, according to an AFP tally of official Israeli figures.
The militants also seized about 250 hostages, around 132 of whom Israel says are still in Gaza.
Israel vowed to crush Hamas and launched a relentless military offensive on the densely populated Palestinian territory.
Gaza's Hamas-run health ministry says the Israeli bombardments and ground offensive have killed at least 26,250 people in under four months -- about 70 percent of them women and children.