US President Barack Obama's Republican foes on Tuesday launched a fresh campaign for reform at the United Nations, with a key leader urging Washington to withhold contributions as leverage.

Republican Representative Ileana Ros-Lehtinen, the new House Foreign Affairs Committee chair, said the United States contributed more than six billion dollars in 2009 only to see a bloated, inefficient and corrupt body.

"We should be conditioning our contributions on 'reform first, pay later," an absent Ros-Lehtinen said in a statement read out by Representative Jean Schmidt, who addressed a committee hearing on UN reform.

US President Barack Obama's administration took office arguing the contrary, that it was necessary for the United States to pay its arrears in order to win back influence in the world body.

Ros-Lehtinen, who was in Florida caring for a seriously ill mother, promised to reintroduce legislation that conditions US "contributions on real, sweeping reform, including moving the UN regular budget to a voluntary funding basis.

"That way, US taxpayers can pay for the UN programs and activities that advance our interests and values, and if other countries want different things to be funded, they can pay for it themselves," Ros-Lehtinen said.

Saying the United Nations is unable to reform itself, she said the UN Development Program (UNDP) has failed to introduce the changes needed to prevent itself from being exploited again by a North Korean regime that selects its staff.

Claudia Rosett, journalist in residence for the Foundation for Defense of Democracies, testified against the UNDP at the hearing entitled "The United Nations: Urgent Problems that Need Congressional Action."

"You had North Korean employees handling the checkbook and the accounts. In Pyongyang, you had transfers on behalf of other agencies via an entity tied to North Korean proliferation," Rosett told the panel.

"You had the import of dual use items into North Korea," she said.

But UNDP spokesman Stephane Dujarric said both a Senate panel and an investigatory panel of non-UN officials documented "that UNDP accounted for funds used in its programs in North Korea."

The panels established "that they were used for the limited purposes for which they were intended," mainly relating to farm production, Dujarric said in a statement.

"Ms. Rosett?s suggestion that millions of dollars were diverted to North Korean military purposes are simply fanciful," he charged.

Dujarric also said UNDP has applied unprecedented safeguards to hiring candidates in a country where there is no open labor market.

Brett Schaefer, a scholar at the conservative Heritage Foundation think tank, testified that "if Congress wants reform, it must heed the history and demand quick action and link specific reforms to financial withholding.

"The UN may have five official languages, but the bottom line speaks loudest," Schaefer said.

Ros-Lehtinen's bill calls for the United States to shun the UN Human Rights Council and to withhold an amount of UN dues equal to what it would contribute to the panel until the US State Department certifies that the council does not include countries regarded by Washington as major human rights abusers.

"We shouldn't give a penny to the UN until they disband that human rights council and completely overhaul it and completely reform it," Republican Representative Steve Chabot told the panel.

The bill, which would also have to pass the Senate, also calls for restrictions on US contributions to the UN nuclear watchdog to ensure that countries like Iran and Syria do not receive nuclear-related assistance as long as they are on a US list of state sponsors of terrorism.

Ros-Lehtinen's proposal would also call for sweeping changes in the way the UN peacekeeping efforts are planned, managed, run and assessed, according to a summary from her office.