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.