One was quickly picked up by a US military helicopter. The other is said to be "safe" after being rescued by Libyan rebels.
The US miltary said their forces were in the process of having him recovered.
The crashed plane was discovered by a Telegraph journalist reporting in and around Benghazi, the rebel-held city.
The US military confirmed that one of its jets had crash landed but said that it had not been shot down.
Vince Crawley, a spokesman for the US military's Africa Command, said that one crewman had been recovered and one was "in process of recovery".
Crawley said the crash occurred "overnight." He declined to give the location of the incident and also would not say how the rescued crewman was picked up.
This is the first coalition aircraft to have crash landed during the Libyan conflict following the third night of air strikes.
Later, Ministry of Defence spokesman Major General John Lorimer said that the allied operations had stopped Col Gaddafi's assault on Benghazi in its tracks.
He said that RAF Tornados yesterday flew a reconnaissance sortie to look out for signs of Col Gaddafi's ground troops threatening Libyan civilians, before joining Typhoons at Gioia del Colle on completion of their flight.
The Typhoon patrol of the no-fly zone yesterday was the first time the RAF has used the plane in enemy airspace, he added.
Both Tornados and Typhoons were supported by Awacs surveillance aircraft and VC10 refuelling planes.
Maj Gen Lorimer told a briefing in London: "A formation of Tornado GR4 aircraft flew south from RAF Marham. Unlike their previous sorties on Saturday and Sunday, which were focused on Libyan military command and control facilities and air defence infrastructure, their mission yesterday was an armed reconnaissance sortie to protect directly the local population from attacks by Colonel Gaddafi's ground forces.
"With their state-of-the-art lightning targeting pods and a variety of precision-guided munitions, the Tornados are very well equipped to identify any emerging threats on the ground and to deliver a dynamic and effective response.
"On completion of their mission, the Tornados joined the Typhoon forward base at Gioia del Colle."
Assessing the overall impact of the coalition operation, he added: "At this time, it would not be wise to disclose to Colonel Gaddafi precisely how well we believe we have performed in degrading his command and control network and his integrated air defence system.
"But on a broader level, we have the best possible indication that this operation is having a very real effect - namely, the protection of Benghazi from Colonel Gaddafi's forces.
"Last Friday, regime troops were on the outskirts of Benghazi... Colonel Gaddafi vowed that his men would be going house to house, room to room, to burn out the opposition. Libyan troops were reportedly committing atrocities in outlying areas of the city.
"The military intervention to enforce UNSCR (Security Council Resolution) 1973 has stopped that attack in its tracks.
"That is not to say that all threat to innocent life in and around Benghazi and other cities has been wholly removed. It has not."
