James Rubin, a spokesman for the State Department, acknowledged that Mr Ocalan would probably not be extradited to Turkey, as Washington had initially urged.
But the US and its allies were reviewing a "full range of options" to bring Mr Ocalan to justice.
Yesterday Turkey decided to pull the plug on two Italian state-run cable television channels, underlining its anger at Rome's refusal to extradite Mr Ocalan, head of the Kurdistan Workers' Party (PKK).
Rather than fault Italy, Mr Rubin praised Rome for "accepting international responsibility" to arrest him. But he also said "the PKK is a terrorist organisation and Ocalan must be held accountable for his role in the PKK's terrorist activities."
Yesterday Turkey's main legal Kurdish party said thousands of its members had been detained in police raids since the arrest of Mr Ocalan.
Italy's reluctance to extradite the PKK leader has enraged Turks. The government holds the PKK responsible for more than 29,000 deaths in a 14-year campaign for self-rule in south-eastern Turkey.
Zeynettin Onay, a board member of the People's Democracy Party (Hadep), said: "A total of 3,064 of our members have been detained ... in the past 10 days." Hadep advocates a peaceful solution to the conflict which has ravaged the south-east.
On Saturday a retired teacher and Hadep member died after an attack by extremists who seized him from police custody in the western town of Izmit. - ReutersReuse content