In Washington, US State Department spokeswoman Victoria Nuland told reporters that "we are very concerned about the case of Mr al-Khawaja, particularly with regard to his health."
She added that Jeffrey Feltman, the assistant secretary of state for Near East affairs, and diplomats at the US embassy had contacted Bahrain about the case.
"We are in touch with the Bahrainis and with our international partners, and we are urging a humanitarian solution," Nuland said.
Denmark has asked Bahrain to send Khawaja, who is also a Danish citizen, to the Scandinavian country. Bahrain's official news agency BNA reported on Sunday that Manama had rejected the request.
But Danish papers quoted the head of the foreign ministry's consular service, Ole Engberg Mikkelsen, as saying that "a (formal) reply will come through diplomatic channels and not via a news agency or Twitter."
Mikkelsen said he did not know when Manama would reply officially.
"Unfortunately there is not much time. It is a case where the clock is ticking," he said. "We are continuing our efforts to convince Bahrain that it is in everyone's interest that he be extradited."
Front Line Defenders, a Dublin-based NGO, warned that Khawaja could now die in jail, ....