NATO warships stopped Muammar Gaddafi forces today from laying anti-ship mines in Misrata’s harbour, the alliance said, accusing the regime of trying to disrupt the flow of aid to the besieged city.

“The sea-mines were being laid two to three kilometres offshore and in the approaches to Misrata by deliberately sinking the inflatable boats on which they were being carried,” NATO said.

Three mines were found today and were being disarmed, the 28-nation alliance said.

NATO warned Misrata port authorities, who closed the facility, prompting the cancellation of the arrival of two humanitarian ships, the statement said.

“The mining of a civilian port by pro-Gaddafi forces is clearly designed to disrupt the lawful flow of humanitarian aid to the innocent civilian people of Libya,” said Italian Navy Vice Admiral Rinaldo Veri.

The move by Muammar Gaddafi’s forces was “another deliberate violation” of the UN Security Council resolution which demands that Libyan authorities allow the rapid and unimpeded passage of humanitarian assistance.

“NATO forces are now actively engaged in countering the mine threat to ensure the flow of aid continues,” said Veri, who is responsible for the maritime forces involved in NATO’s Operation Unified Protector.

He urged civilian shipping companies to continue to coordinate their movements with NATO in order to provide for the safe transit of shipping in the region.

Mr Gaddafi’s regime threatened to attack any ship entering Misrata, insisting aid be sent by road and under Libyan army supervision, state television said.

With Gaddafi forces laying siege outside the shell-shocked city, Misrata relies heavily on its port for the delivery of food via aid ships.

British Brigadier Rob Weighill, director of NATO operations in Libya, said earlier that the discovery of the mines shows Mr Gaddafi’s “complete disregard for international law and his willingness to attack humanitarian delivery efforts”.

While NATO has helped the rebels expel regime forces from Misrata, Brigadier Weighill said it was too soon to say the insurgents were winning the battle for Libya’s third largest city.

“We have pushed pro-Gaddafi forces back and anti-Gaddafi forces boast control of most of the city. Due in large part to NATO’s mission successes to date, Gaddafi forces have not taken the city,” Brigadier Weighill said.

“But pro-Gaddafi forces continue to shell the citizens of Misrata with longer-range artillery, mortars and rockets, indiscriminately firing high explosives,” he said.

The rebels have “expanded their perimetre significantly over the past week” and “are putting up a very spirited fight”, Brigadier Weighill added.

He added, however, that “to suggest that they are winning would perhaps be over optimistic”.

NATO is supporting anti-Gaddafi forces trying to protect the population and facilitate the movement of humanitarian assistance through the harbour, Brigadier Weighill said.

“I would suggest that without NATO support as it is at the moment, certainly the anti-Gaddafi forces would have struggled to have maintained that perimetre and to have taken as much ground as they have,” he said.

“The degree to which humanitarian assistance has come into the harbour and the evacuation of many people would not have been able to take place.”