Washington – The United States expressed deep concern on Friday over the recent arrests of non-violent activists in Indonesia's rebellious region of Aceh and the treatment of a leading activist.

"This is the latest in a series of actions apparently intended to intimidate independent observers who would be in a position to monitor and report on serious human rights abuses in Aceh," the US State Department said in a statement.

Last year Indonesia rejected accusations it had clamped down on freedom of expression and the foreign media in the province of Aceh.

The State Department said it was also concerned about reports that police beat Muhammad Nazar, head of the Aceh Referendum Information Center, during a February 19 interrogation.

His wife and his lawyer have not been allowed to see Nazar, the State Department said.

"We continue to believe that the Aceh conflict is not amenable to solution by use of military force, including the imposition of martial law," the State Department said.

"We urge the Indonesian government to handle cases involving civil society activists with the utmost respect for their legal rights," it said.