Gaddafi's troops have been shelling rebels inside several western cities [EPA]

The Libyan government has announced that its forces took control of Misurata's port and warned rebels in the besieged city they faced further bloodshed unless they handed in their weapons within four days.

Mussa Ibrahim, a spokesperson for Muammar Gaddafi, also urged foreign fighters to leave the country or "[we will] finish you off".

"We will fight for Misurata soldier by soldier, young man by young man, young woman by young woman," he said on Friday.

NATO said there is no evidence to support such claims.

 "We are closely monitoring the situation around Misurata and anti-Gaddafi forces continue to expand their perimeter around Misrata," a NATO official told Reuters news agency.

"(NATO) denies this assertion and finds the statements to lack credibility. They don't relate to the actual situation on the ground," the official said.

Earlier on Friday NATO warships said that they had stopped Gaddafi forces from laying anti-ship mines in Misurata's harbour, accusing the regime of trying to disrupt the flow of aid to the city which has been besieged for two months.

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

Three mines were found early on Friday and were being disarmed, the 28-nation alliance said.

Libya's government threatened to attack any ships approaching Misurata.

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

Responding to diplomatic tensions with neighbouring Tunisia after fighting spilled over the border, Ibrahim blamed the rebels for border violations and pledged respect for Tunisia's sovereignty.

He said Libya that was co-ordinating with the Tunisian government to prevent a disaster on the border.

Earlier on Friday, pro-Gaddafi forces clashed with Libyan rebels, Libyan refugees and Tunisian civilians in the Tunisian border town of Dehiba, prompting Tunis to issue a diplomatic rebuke.

Tunisian troops detained and disarmed pro-Gaddafi fighters and then returned them to the Libyan side of the border, Al Jazeera's Anita McNaught reported from the Tunisian frontier on Friday.

Tunisia summoned Libya's ambassador to protest against the incursions on Friday afternoon, Radhouane Nouicer, the country’s Tunisian deputy foreign minister, told Al Jazeera.

"We summoned the Libyan envoy and gave him a strong protest because we won't tolerate any repetition of such violations. Tunisian soil is a red line and no one is allowed to breach it," he said.

Source: Al Jazeera and agencies