* Rebels claim road to airport bombed
* Rebels say firefight with mercenaries
* Explosions started early in morning (Adds additional quotes, details, byline)
By Mohammed Abbas
BENGHAZI, Libya, March 19 (Reuters) - Explosions shook the Libyan city of Benghazi early on Saturday while a fighter jet was heard flying overhead, and residents said the eastern rebel stronghold was under attack from Muammar Gaddafi's forces.
"The explosions started about 2 a.m. Gaddafi's forces are advancing, we hear they're 20 kms (12 miles) from Benghazi," Faraj Ali, a resident, said.
"It's land-based fire. We saw one aircraft," he added.
Libya had declared a unilateral ceasefire on Friday after the United Nations Security Council authorised a no-fly zone over Libya, but the United States said the ceasefire was not being respected.
Elsewhere in the city, rebels also reported skirmishes and strikes by Gaddafi forces.
"Fighter jets bombed the road to the airport and there's been an air strike on the Abu Hadi district on the outskirts," Mohammed Dwo, a hospital worker and a rebel supporter, told Reuters.
He was speaking at the scene of an apparent firefight between rebels and what they claimed were two mercenaries who had infiltrated the city and were driving in a car which they said contained a crate of handgrenades.
The two men, in civilian clothes, had been shot and killed and rebels produced blood-soaked identity papers they said showed them to be of Nigerian nationality.
"We were sitting here and we received gunfire from this vehicle then we opened fire and after that it crashed," rebel fighter Meri Dersi said.
Jamal bin Nour, a member of a neighbourhood watch group, told Reuters he had received a call to say government forces were landing by boat, but it was impossible to confirm the information.
The city has been so rife with rumours and hearsay that it is virtually impossible to verify due to lack of communications.
(Writing by Michael Roddy; Editing by Sanjeev Miglani)
(Michael Roddy, London newsroom +44 207 542 7923)
Our Standards: The Thomson Reuters Trust Principles.