MISRATA, Libya — Libyan rebels broke out toward Tripoli on Monday from the opposition-held port of Misrata 140 miles to the east, cracking a government siege as fighters across the country mounted a new offensive in their 4-month-old revolt against Moammar Gadhafi.

The rebels gained a diplomatic boost as well when the visiting German foreign minister said the nascent opposition government was “the legitimate representative of the Libyan people.” Guido Westerwelle was visiting Benghazi, the capital of the rebel-held east of the country, to open a liaison office and hand over medical supplies.

He stopped short of full diplomatic recognition of the Transitional National Council, as has the United States, awaiting the ouster of Gadhafi from his more than 40-year rule in the oil-rich North African country.

Germany has refused to participate in NATO airstrikes in Libya and withheld its support for the United Nations resolution that allowed the attacks.

What started as a peaceful uprising against Gadhafi has become a civil war, with poorly equipped and trained rebel fighters taking control of the eastern third of Libya and pockets of the west.

But the fighting had reached a stalemate until last week when NATO began the heaviest bombardment of Gadhafi forces since the alliance took control of the skies over Libya under a U.N. resolution to protect civilians from Gadhafi’s wrath. NATO has been pounding Gadhafi military and government positions with increasing vigor and the rebels are again on the move.

In the major fighting near Misrata on Monday, an Associated Press photographer at the rebel front lines said they had pushed along the Mediterranean Sea to within six miles of Zlitan, the next city to the west of Misrata. A rebel commander said his forces, using arms seized from government weapons depots and fresh armaments shipped in from Benghazi, planned to have moved into Zlitan by today.

Ali Terbelo, the rebel commander, said other opposition forces already were in Zlitan, trying to encircle Gadhafi troops.