There should be "proper accounting" of what British special forces are doing in Libya, the chairman of the Commons foreign affairs committee has said.
Crispin Blunt's call comes after the Times reported that UK troops fired a missile to destroy a truck packed with explosives by Islamic State militants.
Mr Blunt said it was "not surprising" but there should be "proper accounting for our strategy to Libya".
The Ministry of Defence does not comment on special forces operations.
The attack helped Libyan militias to halt IS's advance on the city of Misrata earlier this month, The Times reported.
"The convention that we don't comment on special forces operations or seek parliamentary authorisation will be undermined if they are used as conventional forces," Mr Blunt said.
He told the BBC: "I don't think it is particularly controversial that special forces should be taking on the forces of Daesh, the Islamic State."
It was "certainly not a surprise" because King Abdullah of Jordan gave a briefing to US congressional leaders, which was then leaked, that British and French forces were operating in Libya, he added.
"There should be proper accounting for our strategy to Libya. Explain why British special forces are taking part in that strategy and the kind of role you would expect them to play [while] protecting their capacity for operations," he went on.
He said discussion was needed between the Commons government and the foreign affairs and defence committees.
The BBC understands that British special forces - units from the SAS and SBS who operate in small teams - have been in Libya for more than a year, even though officially the government insists there are no British boots on the ground, defence correspondent Jonathan Beale said.
Last month a spokesman for the Foreign Office said the UK was focused on training Libyan security forces to provide security for its newly-appointed unity government, but had no plans to deploy ground troops.
The foreign affairs committee demanded an explanation from the foreign secretary, amid reports the UK was preparing to send 1,000 personnel.
Earlier this year, UN experts said they believed the political and security vacuum in Libya was being exploited by IS, reporting it had "significantly expanded" the territory it controls in the nation and become "increasingly attractive to foreign fighters".