About a dozen Radio Free Europe journalists in the Caucasus nation were arrested and interrogated over the weekend.
"We are alarmed by the government of Azerbaijan's crackdown on civil society," said Jeffrey Rathke yesterday, a State Department spokesman, noting that those arrested had been denied legal counsel during their interrogations.
He added that US Secretary of State John Kerry had raised his concerns during a December 21 call with Azerbaijan President Ilham Aliyev.
The radio station said all the journalists were eventually released without charge, but had been questioned for up to 12 hours.
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Eight other current and former radio station employees were told to report for questioning or face detention.
This month, Ramiz Mehdiyev, who heads the Aliyev administration, accused journalists of treason and of working for foreign security services.
Azerbaijani prosecutors have in recent months staged raids on other foreign-funded groups, including the Baku offices of the Washington-based National Democratic Institute, which was eventually shut down.
Azerbaijan comes 160th out of 180 in a global press freedom ranking compiled by Reporters Without Borders.
Headquartered in Prague, RFE/RL is financed by the US Congress and broadcasts in 21 countries in Eastern Europe, Central Asia and the Middle East.
The network is rooted in a Cold War program started by the United States to counter Soviet propaganda.