Turkey's prime minister has given warning that his government could ban social media networks YouTube and Facebook after a number of online leaks added momentum to a growing corruption scandal.

Recep Tayyip Erdogan has already tightened his government's grip over the internet, generating criticism at home and abroad about rights in the country.

"There are new steps we will take in that sphere after March 30 ... including a ban [on YouTube, Facebook]," Erdogan told private ATV television in an interview late on Thursday.

His ruling Justice and Development Party, or AK Party, has come under mounting pressure since last week, when audio recordings were leaked in which Erdogan and his son allegedly discuss how to hide vast sums of money.

He dismissed them as a "vile" and "immoral" montage by rivals in the lead-up to crucial local elections on March 30.

A series of other online leaks showed Erdogan meddling in trade deals and court cases.

He has accused loyalists of Fethullah Gulen, an influential Muslim leader based in the US, of using his influence in the judiciary and police to engineer a high-level corruption investigation targeting the government since mid-December.

Gulen denies the charge.

Hope for jailed officers

In a related development on Thursday, Turkey's Constitutional Court backed former army chief Ilker Basbug's attempt for release from a life jail sentence.

The ruling paves the way for Basbug's possible release by a lower court and could be a precedent for more than 200 other defendants jailed for their alleged roles in the Ergenekon conspiracy against Erdogan's government.

Basbug has been held in Silivri prison near Istanbul for 26 months in connection with the Ergenekon case, a trial which helped tame Turkey's once all-powerful military.

The five-year trial, which reached a verdict last August, was key to a decade-long battle between Erdogan's Islamist-rooted AK Party and a secularist establishment that had led modern Turkey from its foundation by Mustafa Kemal Ataturk.

The Constitutional Court said the failure of the lower court to publish its detailed verdict on the case and send it to the appeals court had violated a clause concerning personal freedom.

"It was decided ... to send to the [lower] court a request to do what is necessary in ruling on the applicant's release demand," the ruling on the court website said.

It was not clear why the detailed verdict had still not been completed.

Cemil Cicek, parliamentary speaker from the AK Party, praised the ruling as a triumph of judicial reforms which have been pushed through parliament in recent years.

Gulen's influence

Erdogan is widely believed to have relied heavily on Gulen's influence in breaking the power of the army, which carried out three coups in Turkey between 1960 and 1980 and forced an Islamist-led government from power in 1997.

Gulen's critics say his followers were instrumental in bringing to court the Ergenekon case and another alleged conspiracy, dubbed Sledgehammer.

Erdogan mooted in January the retrial of those convicted of trying to overthrow him in an apparent bid to discredit those in the judiciary he saw as concocting the scandal.

He has responded to the corruption investigation by purging police and passing laws to increase his grip over the internet and the judiciary.

Yalcin Akdogan, Erdogan's top adviser, said the military had been the victim of a plot and that the army subsequently filed a criminal complaint over the cases, arguing that evidence against serving and retired officers had been fabricated.

Last month, the government pushed through parliament a law completing the abolition of the special authority courts which tried the Ergenekon defendants and several hundred military officers in the Sledgehammer conspiracy.

President Abdullah Gul approved that law on Thursday.