Prime Minister David Cameron clashed with a senior Conservative MP as he defended the investigation into a UK drone strike in Syria.
Andrew Tyrie asked why military aspects of the operation were excluded from the probe carried out by the Intelligence and Security Committee (ISC).
The PM said the UK was currently engaged in a military operation and the ISC was set up to look at intelligence.
He also defended his claim of 70,000 "non-extremist" moderate Syria forces.
The bad tempered-exchanges with Mr Tyrie came as Mr Cameron was questioned on Syria by the Commons Liaison Committee.
In September, the PM announced that two British Islamic State jihadists, Cardiff-born Reyaad Khan and Ruhul Amin, from Aberdeen, had been killed by a UK drone strike in Syria.
MPs have since voted to authorise UK air strikes in the war-torn country.
Mr Tyrie, who chairs the committee, asked whether the investigation into the strike would be seen as "incomplete" or even "meaningless" if it could not include its military background.
The PM said he did "not agree with this for a moment".
MPs cannot oversee current military operations, he said, telling Mr Tyrie the UK was currently engaged in an operation against a terrorist group that intends to "blow up, kill and maim our citizens".
The strike was "necessary and proportionate", he added.
"That's what is going on," he said, adding that "if you don't think there is a cell of people sitting in a cell in Raqqa who are planning to try and do damage to this country then you don't know what you are talking about".
After the committee meeting, Mr Tyrie released a statement urging the prime minister to change his mind and allow a "proper inquiry".
"On the basis of today's evidence, the Intelligence and Security Committee will not be able to do a thorough job," he said.
Until the ISC can examine military aspects of the strike, he said, it will not be able to reassure Parliament and the public that the strikes were "necessary and proportionate".
'Not impeccable democrats'
Mr Cameron makes regular appearances before the Liaison Committee, which is made up of select committee chairmen.
He was grilled by defence committee chairman Julian Lewis on why he would not provide more details of the 70,000 troops he described as "non-extremist opposition fighters".
The figure had been provided by the Joint Intelligence Committee, he said, and he did not want to give Syrian President Assad a list of the groups he should be targeting.
They are not all "impeccable democrats", he said: "Some do belong to Islamist groups and some belong to relatively hardline Islamist groups."
The PM also said he was prepared to take another look at offers to take in Syrian refugees made by individuals including Archbishop of Canterbury Justin Welby and former Labour minister Yvette Cooper - after home affairs chairman Keith Vaz said they had been rejected as they had "not been cleared".