The chief weapons inspector, Richard Butler, wrote to Mr Ritter, saying he had violated his United Nations contract by making public information he had received through his UN job.
It is unclear whether the UN will take any legal action against Mr Ritter.
Mr Ritter, who led the UN Special Commission (Unscom) team in charge of disarming Iraq, resigned in August saying it was no longer possible to do his job.
Political intervention
The 37-year-old former marine accused UN Security Council members America and Britain of failing to deal firmly with Iraqi obstruction of the weapons teams.
He also said Washington had intervened several times to try to influence the timing and targets of some inspections.
Since the revelations, Mr Ritter has continued to speak out publicly several times on Iraq's weapons capability.
Praise for Israel
On Tuesday, the Israeli newspaper Ha'aretz quoted Mr Ritter as saying that Israeli intelligence provided essential help to inspectors in unmasking Iraq's concealment of chemical, biological and nuclear weapons programmes.
"I can honestly say that if it weren't for Israel, the Special Commission would not have been able to carry out the anti-concealment effort," Mr Ritter was quoted as saying.
Meanwhile, the UN Secretary-General, Kofi Annan, said he believes he is making progress persuading Iraq to resume co-operation with the weapons inspectors.
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Inspector condemns UN
(02 Oct 98 | World)
Weapons inspector blasts Britain
(27 Sep 98 | UK)
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