MILAN, Italy?A small plane with only the pilot on board slammed into the 25th floor of a landmark skyscraper Thursday, killing at least four people and injuring 60. The interior minister said the crash appeared to be an accident.

In Washington, a senior Bush administration official, speaking on condition of anonymity, said Italian officials had told the United States that a mechanical problem not related to terrorism caused the crash. The pilot had sent out a distress call, saying he had landing gear problems.

Some eyewitnesses reported that the plane was on fire before hitting the 30-story building in the downtown area.

It was the second time since the Sept. 11 terror attacks that a plane has struck a high rise building.

The Rockwell Commander aircraft, en route from Switzerland on a 20-minute flight to Milan, punched a hole in the 25th floor, gutting two entire floors.