MISRATA, Libya: A NATO airstrike has killed 12 rebels in the besieged city of Misrata in the latest friendly fire incident in Libya's chaotic battlefield, a doctor in the city said Thursday. The airstrike was on Wednesday, the second day of intense fighting around Misrata's Mediterranean port, the city's only lifeline to the outside world. A steady stream of boats have been bringing in humanitarian aid through the port and ferrying out hundreds of wounded civilians and foreign migrant workers who were trapped when the fighting broke out two months ago. Dr. Hassan Malitan said he believed the attack was a mistake but insisted it was caused by NATO aircraft. He said the attack came moments after he and another doctor visited a site where rebels were holed up in a building about three miles (five kilometers) east of the port. "We drove about 200 meters (yards) and we heard a huge explosion that shook the earth," Malitan said. He said he looked back and saw smoke rising from where they had just sat with the men. As he and the other doctor began slowly driving back toward the building, a second missile crashed into it, Malitan said. "We started crying and screaming out their names," he said. "It was clear that the missiles came from the sky and we heard the airplane," he said. Malitan said he was surprised to see rebels so far east, and said they assured him that they had been in contact with NATO forces about their location. There was no immediate comment from NATO. Forces loyal to Moammar Gadhafi had been crowding around that area, a coastal road that leads from the capital, Tripoli, to the port. NATO forces targeted them in pummeling airstrikes on Tuesday and Wednesday in an attempt to halt an advance on the port. Gadhafi's forces hit different parts of Misrata throughout the day Tuesday with a near-constant barrage of heavy shelling and rocket fire. By Wednesday, residents said the bombardment had eased some, though fighting went on. Misrata is the only city in government-controlled western Libya where rebels have been able to hold out against a two-month siege by some of Gadhafi's best trained forces. Aid agencies and human rights groups have sounded alarm bells about a growing humanitarian crisis inside the city and NATO has publicly acknowledged it needs to do more to protect civilians in Misrata. But the coalition has also talked about the difficulties of targeting Gadhafi's forces around the city, saying they are mixing in with civilians to make it more difficult to identify them. Also Thursday, a senior U.N. official warned that massive food shortages will also hit Libya within two months unless stocks are replenished and distribution networks are supported. The World Food Program's regional director for the Middle East and North Africa, Daly Belgasmi, said current stocks might last only 45 to 60 days, after which many people will be forced to cut back on meals. He said rising fuel prices and lack of hard currency are making it hard for Libya to import food. Adding to Libya's woes, the private economy was hit by the exodus of foreigners who worked in food production such as bakeries. Belgasmi said government-run distribution networks have also come under pressure due to the conflict.