Journalists for AFP news agency saw two craters of some four metres across and five metres apart near a road junction, after Monday's shelling.
Rebels said there had been no casualties, but the attack on Ajdabiya is seen, from the rebels' viewpoint, "as the last line of defence," said Al Jazeera's Tony Birtley, reporting from Benghazi.
Meanwhile, Gaddafi has reportedly offered an amnesty to rebel fighters if they agree to lay down their arms, Libyan state television reported on Monday.
Al Jazeera's correspondent in the capital Tripoli said the offer will play on very anxious rebel forces who don't know how they are going to be able to put up a fight against Gaddafi's forces, given the overwhelming superiority of his military forces.
"There is an enormous degree of anxiety. It's an all or nothing game now," Anita McNaught said.
"If the rebels do not manage to hold out against Gaddafi and establish some kind of protective zone in the east of the country it is almost certain there would be in the wake of this some dreadful purge of those who dared to raise their hands against the Gaddafi administration.
"People know that unless they are able to in some way keep Tripoli at bay that the alternative is almost too awful to contemplate. Those fears apply equally in Tripoli; they are just not expressed as opening as they are in the east."
'Final phase'
On the battle field, rebel fighters say they have re-taken parts of the oil town of Brega and captured Gaddafi troops - but government forces contest that claim, saying that they are now in control of it.
Fighting has also reportedly resumed in the towns of Ajdabiya and Zuwarah.
General Abdel Fatah Yunis, a rebel commander who resigned as Gaddafi's interior minister soon after the uprising began in mid-February, said that Ajdabiya, little over 100 kilometres to the west, was "a vital city".
"It's on the route to the east, to Benghazi and to Tobruk and also to the south. Ajdabiya's defence is very important... We will defend it," he told reporters.
From Ajdabiya one road runs north along the coast to Benghazi, Libya's second city, with a population of one million, which the rebels have made their capital.
Another road goes straight across the desert eastward to the oil port of Tobruk, which to date has given rebels full control up to the Egyptian border.
Al Jazeera's Birley said "Gaddafi forces are advancing and It seems that fighting is carrying on and coming close to Benghazi.
"It seems like we are entering the final phase of the conflict but whether this revolution will fail or succeed, that will only be determined in the coming weeks."
Meanwhile, the Reuters news agency reports that France was stepping up efforts on Monday to persuade world powers to impose a no-fly zone over Libya.
France said it would consult other powers "in the coming hours" to try to set up such a zone to assure the protection of civilians "in the face of the terrible violence suffered by the Libyan population".
The Arab League's weekend call on the United Nations to impose such a zone satisfies one of three conditions set by NATO for it to police Libyan air space.
The UN Security Council is meeting on Monday to consider options on Libya but no resolution expected yet.
International delay
However, analysts say that by the time the international community agrees on a response to Gaddafi's onslaught against a popular revolt, it could all be over.
"The international community is dragging its feet," Saad Djebbar, a London lawyer and expert on Libyan affairs, told the Reuters news agency.
"The diplomatic pace is very slow. There is an urgency to act quickly before those people are finished off by Gaddafi's forces."
"The international community has to act now - not only to protect Benghazi from an onslaught but because of what it means for the rest of the world if Gaddafi is allowed to remain the leader of Libya," said Geoff Porter, a US-based political risk consultant who specialises in North Africa.
Speaking to Al Jazeera, Tarik Yousef, a senior research fellow at the Dubai school of government said that, "What has been missing is a strong sense of what the US wants to do.
"They need to sort through a lot of ideas they have about a post-Gaddafi Libya, but the time that they are taking, I am afraid it will come at a great cost to Libyan civilians."
'Arm the rebels'
Britain has also been pushing for the imposition of a no-fly zone to shield Libyans from Gaddafi's air power.
William Hague, British foreign secretary said that international powers should consider the option of arming Libyan rebels and take swift action to prevent Gaddafi forces from crushing a popular rebellion.
Hague said it would be a nightmare for Libya's people if Gaddafi managed to hold on to power.
"If Gaddafi went on to be able to dominate much of the country, well this would be a long nightmare for the Libyan people and this would be a pariah state for some time to come,"Hague told BBC Radio.
Of the UN's veto-yielding members, China has been against the imposition of a no-fly zone, while Russia has appeared reluctant and the United States, Germany and Italy have taken a cautious line on intervention.
However, Dmitry Medvedev, Russian president has banned Gaddafi and 15 members of his family and immediate circle from Russia and from carrying out financial transactions in the country , the Interfax news agency reported.
Besides the ruling family, the financial restrictions also apply to the head of Libya's military intelligence service, who is Gaddafi's brother-in-law, Interfax said.