Muammar Gaddafi's regime is on the run, a NATO official said, as alliance jets blasted Libya's capital and Russia on Wednesday slammed the blitz of Tripoli as a 'grave departure' from UN resolutions.

The senior NATO military official said the Western alliance is shifting into high gear in Libya in a bid to deliver a decisive blow to Gaddafi's government, hitting Tripoli with its heaviest bombardment to date.

Six powerful explosions struck late Tuesday near Gaddafi's residence, targeted a day earlier by intensive NATO air strikes, a journalist said.

Jet fighters could be heard above before three deafening explosions rocked the area of the embattled leader's Bab Al-Aziziya residential compound around 11:00 pm (2100 GMT), followed by three others two minutes later.

The zone came under heavy bombardment overnight Monday lasting more than half an hour, leaving three dead and 150 wounded, according to the Gaddafi regime.

Government spokesman Mussa Ibrahim insisted those strikes targeted a deserted military barracks but instead hit civilians living nearby.

NATO rejected the charge, saying that a strategic vehicle storage facility -- used to resupply the regime forces and instrumental in attacks against civilians -- had been struck.

The NATO official said in Brussels the allies hoped Gaddafi would fall by late June or early July.

"The regime has become very apathetic in the last 15 days. It has lost the military initiative and appears on the defensive, which is a sign that we are on the right path," he said.

"We think that we must speed up and increase the tempo of our operations to let the fruit drop on its own."

After three months of fighting, however, the regime remains entrenched in much of the west, including the capital Tripoli.

Worried about getting bogged down in an endless stalemate, NATO allies, who were divided over going into Libya in the first place and face budgetary constraints, have no choice but to increase the pressure, the official said.

The alliance must "speed up the systematic destruction of Tripoli's military machine with the goal of neutralising Gaddafi's forces for good," he said.

NATO began to turn up the heat last month with almost daily strikes in and around Tripoli, including an evening air raid on April 30 that the regime says killed one of Gaddafi's sons and three grandchildren. NATO has not confirmed the deaths.

Russia's foreign ministry Wednesday called NATO's latest bombings of Tripoli a "grave departure" from UN resolutions on Libya that could lead to a further escalation in violence.

"We clearly see another grave violation on UN Security Council Resolutions 1970 and 1973," the ministry said in a statement.

Russia said the West's attempts to justify the offensive by pointing to the threats being posed to civilians by Gaddafi's regime ignored the danger of the Tripoli government becoming even more entrenched in its stance.

"Air strikes are not stopping the military confrontation between the Libyan parties and only creating more suffering among peaceful civilians," the statement said.

Meanwhile, fighting at a refugee camp near the Tunisia-Libya border left two people dead, while a blaze injured seven others, a source close to the defence ministry said.

Two Eritreans were killed when stones were thrown during a clash with other refugees at the Choucha camp seven kilometres (four miles) from the border, the source told AFP.

Another seven, whose nationality is not known, were injured in a fire started by the Eritreans which destroyed 200 tents.

Thousands of people have fled to the camp since violence broke out in neighbouring Libya in February.