Bahrain's interior ministry said on Monday that jailed activist Abdulhadi al-Khawaja, who has been on a hunger strike for two months, is in "good health" after his lawyer expressed fears he could be dead.
"Abdel Hadi al-Khawaja's state of health is good," the interior ministry said in a statement, adding that the activist had been transferred to a military hospital "for the best medical treatment."
The ministry also said his case was being handled without "political or media pressure and with respect for human rights."
Khawaja's lawyer, Mohammed al-Jeshi, had earlier expressed fears that his client could be dead, after the authorities turned down repeated requests to contact him.
"Authorities have been refusing since yesterday (Sunday) all requests, made by myself and by his family, to visit or contact al-Khawaja," Jeshi told AFP.
"We fear that he might have passed away as there is no excuse for them to prevent us from visiting or contacting him," he said, adding that no more information was available about Khawaja's health.
Jeshi said the last time he contacted Khawaja was on Saturday, a day after he was moved from the interior ministry hospital into a military hospital in Manama.
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.
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Khawaja, a Shiite who was condemned with other opposition activists to life in jail over an alleged plot to topple the Sunni monarchy during a month-long protest a year ago, began a hunger strike on the night of February 8-9.
Bahrain's largest opposition formation Al-Wefaq reiterated its calls for his release on Monday in a statement accusing authorities of "completely ignoring his deteriorating health which has reached a dangerous stage."
Demonstrations in solidarity with Khawaja have multiplied across the tiny kingdom where youth groups organise almost daily evening protests in Shiite villages.
Bahrain's national airline Gulf Air said its page on a social network website was hacked early on Monday. The page was back a few hours later.
Police also used tear gas to disperse hundreds of demonstrators who gathered in the Sanabis district of Manama to demand Khawaja's release, witnesses said.
They made three arrests, the witnesses added.
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, while Al-Wefaq has said refusing a transfer to Denmark amounted to having "signed his death" sentence.