* Poland investigating allegations of CIA jail on its soil
* Rights activists allege deliberate foot-dragging
* Third alleged detainee files complaint with prosecutors (Adds Amnesty International reaction, new alleged victim)
By Christian Lowe and Marcin Goettig
WARSAW, June 12 (Reuters) - Polish prosecutors have extended until October a five-year-old criminal investigation into allegations that the CIA ran secret jails on Polish soil, a case human rights activists say the authorities are deliberately dragging out.
The United States has acknowledged it used a network of facilities in foreign countries to detain al Qaeda suspects in the aftermath of the Sept. 11, 2001 attacks on U.S. cities, though it has never disclosed their location.
Poland is the only one of the alleged hosts of the CIA "black sites" which has a criminal investigation open. If the case goes to trial, it could implicate senior political figures and complicate Warsaw's relations with Washington.
"The general prosecutor decided yesterday to extend the investigation by four months," said Mateusz Martyniuk, spokesman for the prosecutor's office.
Amnesty International campaigner Julia Hall said the extension was part of a pattern of unexplained delays in bringing the case to trial.
"(We are) quite concerned about the numerous delays in the investigation, and, now that the investigation is over five years old, the possible reasons for those delays," she said.
The investigation has already been extended several times. Rights activists say prosecutors have ample evidence to convict former Polish officials of allowing the CIA to operate a jail, but are under political pressure to avoid a trial.
NEW COMPLAINT
The government and prosecutors deny any political interference and say they are committed to a full investigation. The Polish authorities deny the existence of any CIA jail.
Two men who say they were held in a CIA jail in Poland, Saudi-born Abu Zubaydah, and Saudi national Abd al-Rahim al-Nashiri, have been granted the status of victims by the Polish investigation.
A request was filed on Tuesday with Polish prosecutors for a third man to be officially recognised as a victim, said Mariusz Paplaczyk, the man's lawyer.
He says his client, Yemeni national Walid Bin Attash, was held in Poland in 2003. Bin Attash is now in the U.S. military jail at Guantanamo Bay, Cuba, accused of running an al Qaeda training camp in Afghanistan.
Amnesty International on Wednesday released a report which called on prosecutors to bring to justice anyone involved in the alleged CIA facility in Poland, and asked the government not to exert any pressure on the investigation.
"The Polish government knows what happened in Poland and should have the political courage to own up to it," Amnesty's Hall said at the launch of the report in Warsaw.
Human rights groups, citing evidence including flight records and detainees' accounts, say al Qaeda suspects were held in a CIA jail at a secluded intelligence training academy near Stare Kiejkuty in the north of Poland, where they were subjected to interrogation techniques that amounted to torture. (Editing by Raissa Kasolowsky and Alistair Lyon)
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