It is a "disgrace" that British ministers say they did not know US forces had used napalm-style fire bombs in Iraq, according to an ex-Labour MP.
Napalm became infamous during the Vietnam War
Alice Mahon was among MPs told by Armed Forces Minister Adam Ingram earlier this year that the US had said it had not used napalm or similar substances.
Mr Ingram has now told the MPs he has since discovered that Mark 77 fire bombs were used by the US.
Mrs Mahon says the UK should have known what its closest ally was doing.
Napalm is especially controversial because of its use in the Vietnam War.
Ministry of Defence officials say Mr Ingram was acting on the best available information when he answered parliamentary questions to both Mrs Mahon and fellow Labour MP Harry Cohen.
Mr Cohen asked in January whether the firebombs had been used by coalition forces in Iraq.
Mr Ingram replied in a written answer: "The United States have confirmed to us that they have not used Mark 77 firebombs, which are essentially napalm canisters, in Iraq at any time.
"No other coalition member has Mark 77 firebombs in their inventory."
A Ministry of Defence spokesman said: "It was unintentionally misleading because that was the information we had at the time.
"Subsequently we put that right at the first opportunity."
Mr Ingram is understood to have written to Mr Cohen and Mrs Mahon to correct his answers.
Mrs Mahon said it was a "disgrace" if ministers were pleading they did not know what had happened.
"If they did not know, why didn't they know because this was possibly our closest ally," she told BBC News.
She said Mark 77 bombs were simply a more sophisticated version of napalm bombs which still "melt people".
Mr Cohen said Mr Ingram had told him the bombs had not been used in civilian areas but the MP said he was worried they could have been used in Falluja.
There should be a Commons statement and debate on the issue, said Mr Cohen. He is also asking at what point ministers discovered they had been misled by US officials.
On Sunday, Defence Secretary John Reid said American officials in Baghdad had given the wrong information.
He claimed it was "cock up" not conspiracy.
He told ITV's Jonathan Dimbleby programme: "First of all, they didn't use napalm. They used a firebomb. It doesn't stick to your skin like napalm, it doesn't have the horrible effects of that.
"Secondly, we have never used anything that even approximates to what they were using."