Two Reston area residents have told Fairfax County police an armed man who claimed to be an undercover police officer briefly held them hostage Thursday night in a wooded area of the county near Sunset Road.

Police said Thomas A. Huffman, 21, of Sterling Park, and Ellen Fox, 19, of Reston, were sitting in Huffman's parked van when a man dressed in green fatigues and armed with a rifle appeared and tried to trap the van by pushing two abandoned washing machines in front of it.

The armed man, who police said was in his early 20s, identified himself as an officer and ordered the pair out of the van. Huffman demanded to see identification, and when the man couldn't produce it, Huffman told Fox to stay in the van.

Police said Fox drove the van to Reston Avenue, where she flagged down a passing motorist and summoned police. Huffman told police later he managed to escape from the suspect.

Police dogs tracked the suspect to a campsite near the Dulles Access Road, about 400 yards from where the incident occurred, a police spokesman said.

There were no injuries, police said, and a suspect has not been found.