As rebel forces retreat in Libya, the New York Times is reporting that the CIA has sent in teams to identify targets for airstrikes and establish links with the rebels.
The newspaper also cites current and former British officials as saying dozens of British special forces and MI6 secret intelligence service agents are in Libya collecting information on government forces and weaponry.
Several media organisations are reporting from the United States that President Barack Obama has secretly authorised covert assistance to the rebels.
CNN's senior political analyst says that while the US military has denied the presence of troops in Libya, it has been less forthcoming about CIA operatives.
The Reuters news agency, cited by the BBC, reports that Mr Obama recently signed a secret document allowing support to the rebel groups.
The White House has declined to comment on the reports.
Mr Obama has pledged that US troops will not join the effort to eject Libyan leader Muammar Gaddafi but has not ruled out the US arming the rebels.
In interviews with American television networks, he has spoken of applying "steady pressure, not only militarily but also through these other means" to encourage Col Gaddafi to step down.
Threat to sue oil companies
Meanwhile, the Libyan government says it will sue any foreign oil companies that buy oil from the rebels.
The rebels had hoped to start exporting oil within the week to finance their insurgency but have since lost control of two of the oil towns they had previously captured.
The Gulf state of Qatar had agreed to help bring the oil to market.
