The Federal Bureau of Investigation added Liban Haji Mohamed, a naturalized American citizen, to its most wanted list on Thursday and announced a reward of up to $50,000 for anyone who could provide information that could lead to his arrest and conviction. Liban, a former taxi driver in northern Virginia, has been accused by the FBI of providing “material support and resources” to al Shabab, an al Qaeda-linked militant group in Somalia.

An arrest warrant was issued against Liban, 29, in February last year, and was unsealed Thursday by U.S. District Court in Alexandria. Liban’s younger brother Gulet Mohamed had been added in the no-fly list of the U.S. government and he has been challenging the decision for the last four years. Gulet had been detained in Kuwait several years ago and officials had barred him from entering the U.S., Gadeir Abbas, Gulet's attorney, said according to The Associated Press (AP). Abbas added that Liban had aggressively advocated for his brother at the time and claimed that the FBI had started harassing Liban as retaliation.

“Liban Mohamed is believed to have left the U.S. with the intent to join al Shabaab in East Africa. We believe he is currently there operating on behalf of that terrorist organization,” Carl Ghattas, special agent in charge of the counterterrorism division at the FBI’s Washington field office, said in a statement, adding: “It is important for us to locate Mohamed because he has knowledge of the Washington, D.C. area’s infrastructure such as shopping areas, Metro, airports, and government buildings.”

The FBI statement claims that Liban is an “asset” to terrorist organizations because of his knowledge of the American capital. It added that during his time in northern Virginia, Liban was a recruiter for al Shabab, which has claimed responsibility for several attacks in Somalia and Uganda.

A hearing for Gulet’s case is scheduled on Friday. Abbas said that Liban, who left the U.S. in July 2012 according to FBI, may have fled to avoid harassment. He further argued that the timing of the announcement was an attempt to throw out the lawsuit filed by Gulet, AP reported. "We would question the timing of the FBI's placement of Liban on the most-wanted list on the day before a major hearing on the government's authority to maintain the no-fly list," Abbas said, according to AP.