President-elect Joe Biden's brother James is caught up in an FBI investigation, it emerged Thursday - the day after Hunter Biden confirmed he was the target of a federal tax probe.

Agents have asked about James Biden, one of Joe's two younger brothers, during an investigation into a hospital business in Pennsylvania in which he was involved, Politico reported.

The business, Americore, ran rural hospitals and was raided by agents in January after entering bankruptcy. Politico reported that in the course of their investigation, the FBI has asked about James Biden's involvement in the business.

He has been described as its 'principal,' but has disputed that description and his role is the subject of litigation in at least two states. In one court case he was accused of dropping his brother's name to drum up business.

The revelation came after Hunter admitted he was the target of a separate tax investigation by federal prosecutors in Delaware, focused on his extensive - and lucrative - Chinese business dealings.

Republican senator Tom Cotton told Fox News Thursday that there should be a special counsel appointed into both Bidens, alleging that Hunter's investigation stretched into securities fraud as well as tax issue. 

Hunter said in a statement that he was unaware of the investigation until Tuesday and expected to be cleared, although CNN reported that it had asked his spokesman about the investigation on Monday. A grand jury has been sitting in Delaware as part of the investigation.

Federal authorities had paused their investigation into Hunter in the run up to the election.