Europe has become a "happy hunting ground" for foreign intelligence agencies, according to the human rights watchdog, the Council of Europe.
Terry Davis says state immunity should not mean impunity
The council has been investigating claims of illegal detentions and transport of prisoners by the CIA.
Council Secretary General Terry Davis, who presented the report, said safeguards were needed to stop abuse.
His report found no new evidence of secret prisons on European territory. The US says it has not broken any law.
Mr Davis said a number of countries had systems for overseeing their own national security services - such as the UK.
But "hardly any country in Europe has any legal provisions to ensure an effective oversight over the activities of foreign agencies on their territory," he said.
He added that Hungary was an exception and "an outstanding example, where their parliamentary committee oversee both national and foreign security services".
The report follows a request by Mr Davis in November for the Council's 46 member states to submit information relating to suspicions that the CIA had run secret jails in Europe.
He also asked them to reveal anything they knew about secret CIA flights across Europe, in which prisoners are alleged to have been transferred to jails in third countries where they faced torture and other abuses.
US Secretary of State Condoleezza Rice has said suspects are flown abroad for interrogation - a process called rendition. But she has denied that torture is used.
Mr Davis said existing procedures to monitor who and what were passing through European airports and airspace did not provide adequate safeguards against abuse.
He added that the existing rules on state immunity also created "considerable obstacles for effective law enforcement in relation to the activities of foreign agents".
COUNCIL OF EUROPE
Founded in 1949 and based in Strasbourg, France
Forty-six members, 21 of them from Central and Eastern Europe
Set up to defend human rights, parliamentary democracy and the rule of law
Acts as human rights watchdog for Europe
Oversees the European Court of Human Rights
Comprises a decision-making committee of ministers and 630-member parliamentary assembly
"Immunity cannot mean impunity," he said. "Exceptions to state immunity already recognised in the case of torture should be extended to other serious violations of human rights, such as enforced disappearances."
Mr Davis said responses from Italy, Bosnia-Hercegovina, the former Yugoslav Republic of Macedonia and Poland had not been satisfactory and his inquiry would push them for further details.
The European Parliament has also set up a committee to investigate rendition flight claims, which will run alongside the Council's inquiry.
Human Rights Watch has said it has circumstantial evidence suggesting that the CIA transported suspects captured in Afghanistan to Poland and Romania - both of which have denied the claims.
Germany denied any role in the abduction of its national Khaled al-Masri, who says he was seized by US intelligence agents in 2003 and taken to Afghanistan, where he was held for five months and mistreated.