MISURATA, Libya — Military forces loyal to Col. Muammar el-Qaddafi scattered antitank land mines on the port of this besieged city late Thursday night, threatening once more to close the city’s only route for evacuation and supplies, according to accounts of witnesses, photographs and physical evidence collected on the ground.

The land mines were delivered by a Chinese-made variant of a Grad rocket that opens in flight and drops mines to the ground below, each slowed slightly and oriented for arming by a small green parachute, according to an identification of the sub-munitions by specialists who were provided photographs and dimensions of the weapons.

The mines hit the port at 9 or 10 p.m. Thursday, after rockets were heard being fired on the city from the southeast. A short while later, a truck driven by rebels who were patrolling the harbor struck two of them. Both men inside were wounded, according to a port supervisor and one of the victims, Faisal el-Mahrougi, the driver.

Officials and guards said more than 20 mines were distributed in the attack, and remains of at least 13 were observed firsthand. It was not possible to verify an exact number, as many had been destroyed by rebels who, to clear the mines, shot them with rifles, causing them to explode. By nightfall on Friday, the port appeared to have been cleared.

The use of mine-distributing rockets echoed the documented use of cluster bombs here, and underscored anew the Qaddafi government’s efforts to deny the use of the port to the rebels and to international aid organizations. Regarded as highly indiscriminate weapons, land mines are widely banned by the international community, though several nations, including the United States and Libya, have not signed the international convention prohibiting their production and use, and they retain land mines in their arsenals. The convention covers antipersonnel land mines, not land mines designed to destroy vehicles. However, the mine used in this attack, a Chinese Type 84 Model A, shares many of the indiscriminate characteristics of many banned mines.

The use of such mines also introduces a new menace to the city. The Type 84 Model A is fired by a mobile multiple-rocket launcher system that can carry up to 24 rockets containing 8 mines each. The system’s range is slightly more than four miles, according to a publication of Jane’s Information Group.

For months the port in Misurata, on the Mediterranean Sea at the city’s eastern edge, has been essential to the survival of the city. It has been the sole means of resupply and the only point of evacuation for migrant workers and hospital patients, who have been carried to safety by ships, tugs and fishing vessels that have dared enter its channel, at risk of facing a gantlet of fire.

The introduction of what are known as scatterable land mines also marked a fresh escalation of the munitions used by the Qaddafi forces in this siege.

Last month, during the ferocious urban battle for one the city’s main boulevards, the loyalists repeatedly struck the city with Spanish-made cluster munitions. And the city has been pounded by mortar shells, artillery and ground-to-ground rockets throughout.

Rebels have repeatedly spoken of their fears that through shelling or ground attack the loyalists will seize the harbor and try to strangle the city.

This newest threat from Chinese-made mines had not been seen before in this war.

After being released from a cargo canister while the rocket carrying them is in flight, these mines, each weighing roughly seven pounds, fall from the air with legs that extend and join underneath each mine’s body like a spike. This is designed to drive the mine into the soil and stand it roughly vertically — with a shaped charge facing upright.

Each mine has a magnetic proximity fuse set to blast the charge upward into the bottom of any metallic vehicle that passes over it. Each also has an anti-handling device, to prevent removal, and time fuse that causes the mine to self-destruct up to three days after being armed.

The identification was made using a photograph of one of the unexploded mines, along with images of parts of the remnants of several others that were destroyed either by detonating against the truck or by being struck by the rebels’ bullets.

These images were shared with several private organizations, including Human Rights Watch, and with a private-sector ordnance specialist who distributed the photographs to a network of colleagues, who confirmed the munitions’ identification.

The rebels who discovered them said they initially did not know what they were, and they said the mines had been hard to see at night, with their dark green paint. Mr. Mahrougi, the driver whose truck passed over two mines that had settled onto one of the port’s roads, does not remember seeing them as they exploded in rapid succession.

He emerged in stable condition from surgery Friday night for treatment of third-degree burns, a broken left foot and extensive fragmentation wounds to his left arm, leg, abdomen, chest and face.

Mr. Mahrougi had been examining the port’s warehouses and roads after an odd-sounding rocket strike, and amid reports that Qaddafi helicopters had been heard over the city.

“We saw some rockets, and our guards where checking,” a port supervisor said. “And then one of our trucks hit them.”

The official asked not to be identified to protect his relatives in Tripoli from retaliation from the Qaddafi government. According to the lot number stenciled in black paint on one of the mines, the munitions were manufactured in 2009.

Arms sales between China and Libya are not transparent. How and when the weapons were obtained was not immediately clear.