Member states owe the UN about $3.5bn (£2.2bn) for its regular operating budget and peacekeeping operations, its management chief has announced.

Yukio Takasu said after briefing the general assembly’s budget committee that “as a whole, the financial situation of the United Nations is very sound and generally good – except the regular budget”.

The funding gap is just over $950m including about $800m owed by the US, $77m by Brazil and $28m by Venezuela.

The general assembly approved a two-year budget of $5.53bn in December to cover the UN’s regular operations in 2014-15, cutting it for a second successive time.

Takasu said the UN had only $35m in cash for the regular budget, which was “a bit alarming”. It had two reserve funds totalling about $384m but the overall total of $419m was low, he added.

“The regular budget is very tight and we have to watch very carefully,” Takasu said. “We have very small reserves so [the] financial health of the organisation totally depends on how quickly and how much member states can pay to us.”

Member states also owed about $2.6bn to the separate UN peacekeeping budget, Takasu said. France owed the most – $356m – followed by the US, which must pay $337m, and Italy owed about $250m.

An official at the US mission to the UN said those numbers were distorted because the UN’s fiscal year began on 1 January and the American fiscal year on 1 October. The US paid its regular budget assessment at the end of the calendar year in which it was due, the official said.

The official said this discrepancy accounts for $621m of the outstanding dues to the regular budget reported by the UN.

The remaining amounts in the regular and peacekeeping budget are attributable to arrears that date back more than a decade and a half, the official said.

French diplomats said the debt was not unusual as there was always a technical delay of a few months between the time the French government received assessments for UN contributions and the time the funds were made available to pay them.

The UN owes $1.2bn to member states that contribute troops and equipment to peacekeeping operations, which Takasu said was “rather high”. But he said the intergovernmental organisation was going to pay troop-contributing countries $500m in the coming days and more in November and December to bring the amount it owes down to $501m.

Takasu said 29 countries had paid their assessments, which also included payments for UN tribunals and the recent renovation of UN headquarters.