WASHINGTON (AFP) - Police blocked off roads around the Pentagon on Friday and searched the surrounding area after arresting a man with a suspicious backpack in nearby Arlington National Cemetery. FBI spokeswoman, said the man in his 20s was carrying a backpack with "suspicious items and products" but no explosive devices or materials. The backpack "contained a non-explosive unknown material which requires further investigation.... This was not a device and the products in the backpack are inert," she said, without providing further details. She added that a bomb squad had searched a nearby vehicle, a red Nissan, but found no explosives, and that the arrested man had "acted alone." Several media had reported early Friday that a suspicious device had been found in a vehicle near the US military's headquarters, a massive complex south of the capital. Police had closed off several roads around the Pentagon, snarling the morning commute from the northern Virginia suburbs into the capital. The roads were reopened later Friday morning. The US Park Police, which patrols national parks and monuments in the area, said it arrested the man overnight in the Arlington National Cemetery. Park Police spokesman David Schlosser told reporters the heightened security measures were taken after the suspect was "not very cooperative with the answers to what his activities were." US authorities have been on alert for revenge attacks following the killing of Al-Qaeda chief Osama bin Laden in a US raid in Pakistan last month. The global terror network is believed to have been behind the attempted bombing of a US airliner in December 2009, a failed car bomb in New York's Times Square in May 2010 and a foiled parcel bomb plot last October. Authorities declined to comment on whether the suspect arrested on Friday had any connection to the group.