By Thomas Escritt

AMSTERDAM (Reuters) - Prosecutors at the International Criminal Court in The Hague said on Monday there were preliminary grounds to believe U.S. forces committed war crimes in Afghanistan and at secret detention facilities elsewhere in 2003 and 2004.

In a report, prosecutors said there was a "reasonable basis to believe" that U.S. forces had tortured prisoners in Afghanistan and at Central Intelligence Agency detention facilities elsewhere in 2003 and 2004.

"Members of US armed forces appear to have subjected at least 61 detained persons to torture," the prosecutors' office, wrote. It added that CIA officials appeared to have tortured another 27 detainees.

The prosecutors' office, headed by Prosecutor Fatou Bensouda, said it would decide imminently whether to pursue a full investigation.

The results of a full investigation could potentially lead to charges being brought against individuals and the issuing of an arrest warrant. The ICC is a court of last resort, however, meaning it could only bring charges if domestic authorities were not dealing adequately with allegations.

Monday's finding marks a significant step forward in the court's decade-old examination of conflicts in Afghanistan and could draw a sharp response from a U.S. administration that is set to become less internationalist under President-elect Donald Trump.

"These alleged crimes were not the abuses of a few isolated individuals," the report said. "They appear to have been committed as part of approved interrogation techniques in an attempt to extract 'actionable intelligence.'"

The United States occupied and patrolled large parts of Afghanistan during their hunt for the Taliban and al Qaeda forces behind the Sept. 11, 2001, attacks.

Further crimes may have been committed at CIA facilities in Poland, Lithuania and Romania, prosecutors added, because individuals captured in Afghanistan were allegedly transferred to those sites.

The report, covering all the many preliminary examinations being carried out by the court, found grounds to suspect all belligerents, including the Taliban and the Afghan government, had committed war crimes.

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The ICC was set up in 2003 to prosecute the gravest war crimes and crimes against humanity. The United States, which under President George W. Bush was fiercely opposed to the court, is not a member, but Afghanistan, Lithuania, Poland and Romania all are, giving it jurisdiction over crimes committed on their territories.

Under Bush, officials led by U.N. Ambassador John Bolton, now being cited as a potential member of Trump's cabinet, attacked the court and legislation was passed mandating U.S. forces to free any soldiers arrested on the court's authority.

The U.S. Senate Intelligence committee released in 2014 excerpts from a report on the CIA's detention and interrogation program from 2001 to 2006 that it said included torture of detainees.

(Reporting By Thomas Escritt; Editing by Cynthia Osterman)