NATO said forces loyal to Muammar Gaddafi had laid mines on the approach to the harbor, under siege for weeks, and forced a temporary halt in humanitarian shipments, but had not taken control of the port. Libya's government claimed earlier it was in control of the port and that vessels would only be allowed in with government permission.

"NATO forces are now actively engaged in countering the mine threat to ensure the flow of aid continues," NATO said.

Libyan government spokesman Mussa Ibrahim made no specific mention of mines, but said: "We will not allow weapons and supplies to come through the sea port to the rebels.

Libyan state television said government forces had rendered the port non-functional and "any attempt to enter the port will be attacked, regardless of the justifications."

Further west, the war spilled into Tunisia when Gaddafi's forces overran a rebel enclave at the frontier. The Libyan army shelled the Tunisian border town of Dehiba, damaging buildings and wounding at least one person, witnesses said. They said Libyan soldiers drove into the town in a truck chasing rebels.