The Council of Europe said that five years after the September 11 attacks, the world had not been made any safer by subjecting suspects to torture.
Rene van der Linden, chairman of the council's parliamentary assembly, said: "I have no doubt that interrogating suspects using 'alternative procedures' in secret locations beyond the law - an official US government policy as of this week - will not make Americans safer in the long run."
Thomas Hammarberg, the council's human rights envoy, called on governments to ban torture and end the policy of extraordinary renditions of suspects.
"National security services should be based on clear and appropriate legislation providing for adequate safeguards against abuse," Hammarberg said.
In June, the body produced a report accusing European governments of colluding with the CIA in the transfer of suspects to secret US jails.
European Union parliamentarians are to travel to Germany, Britain, Romania and Poland over the next two months as part of an investigation into the council's findings.
They are to visit Germany in September and will travel to London at the beginning of October.
The committee will visit Romania in October and Poland in November to investigate allegations by human rights groups that CIA ran secret prisons there.