The United States is deeply concerned about American Paul Whelan, who is in a Russian jail, White House national security spokesman John Kirby said on Wednesday after Whelan's family said they had not heard from him for a week.

U.S. diplomats have been trying to get more information about Whelan's condition and his whereabouts, Kirby said.

'As we speak this morning, regrettably, we do not have an update specifically about where he is or what condition he's in,' Kirby told reporters in a telephone briefing. 'That deeply concerns us, and we certainly share the anxiety and the concern of the land and family.'

Kirby addressed the issue after Whelan's brother, David Whelan, said the family had become concerned about his whereabouts.

David Whelan said in an e-mail on November 29 that it was unusual that the family did not know the whereabouts of the former U.S. Marine and corporate security executive, who is serving 16 years in the Russian region of Mordovia on charges of espionage, which he denies.

The U.S. State Department has said it has been negotiating with Russia on a potential prisoner swap that would involve Whelan and U.S. women's basketball star Brittney Griner, who is serving nine years in Russia after being convicted on drug charges.

The negotiations appear to be stalled as the Russian side has not provided a 'serious response' to any of the U.S. proposals on a prisoner swap, a senior U.S. diplomat said on November 28.

The penal colony's staff said Paul Whelan was moved to the prison hospital on November 17, a day after a visit by U.S. and Irish diplomats, David Whelan said in the e-mail.

Paul had spoken to his parents every day from the 17th to the 23rd and did not mention the move and had appeared healthy and well to the diplomats, David Whelan said in the e-mail.

"Paul has always mentioned when he's been transferred to the prison hospital,' said David Whelan, adding that the transfers usually have occurred without his request or need for medical attention.

"And he spoke to our parents a number of times after the [penal colony] staff say he was moved, at least as recently as November 23, and never mentioned it," David Whelan said, questioning why his brother has been prohibited from making calls if he is at the prison hospital.

'Is he unable to make calls? Or is he really still at [prison colony] IK-17 but he's been put in solitary and the prison is hiding that fact?' David Whelan asked.

David Whelan added that it was highly unusual that the family did not hear from him on November 24, the U.S. Thanksgiving Day holiday.

Some information for this report came from by Reuters.