By Jill McGivering
BBC State Department correspondent
The US State Department has announced it is withholding $34m (£18m) allocated to the UN Population Fund.
The UN fund denies any money goes towards abortion programmes
State Department officials said the decision was taken because of an ongoing row about the fund's support for China's family planning programmes.
The US says there is a direct link between the UN fund's work and the Chinese practice of forced abortion - an allegation the UN denies.
This is the third consecutive year the money has been withheld.
State Department spokesman Richard Boucher said the administration had no choice.
The Congress-approved payment was not possible under US law because of a direct link between the UN Population Fund's programmes in China and the Chinese government's practice of coercive abortion.
He said the US recognised the fund was trying to help China move towards voluntary family planning.
But, in the meantime, the fund was assisting the Chinese in managing programmes unacceptable to the US.
"These Chinese programmes have penalties that amount to coercion," said Mr Boucher.
"Therefore we feel, by funding these programmes, we would be indirectly helping the Chinese to improve their management of programmes that result in coercive abortion, and that's prohibited by our law."
Officials at the UN Population Fund have reacted with anger.
They deny any of the fund's money goes to forced sterilisation or abortion programmes and cite an internal State Department study two years ago which, they say, failed to find any evidence it did.
Critics of the decision say the money could have protected the health of hundreds of thousands of Chinese women by helping to prevent unwanted pregnancies and reducing the number of deaths of mothers and babies in childbirth.