ISTANBUL: Turkish investigators grilled today more than 40 military figures, including the retired heads of navy and air force, after mass arrests over an alleged plot to oust the Islamist-rooted government.

In the most dramatic move to date against the armed forces, anti-terror police detained the suspects on Monday over a purported plan codenamed “Operation Sledgehammer”, drawn up in 2003 soon after the Justice and Development Party (AKP) came to power. Investigators say the suspects planned to bomb mosques and escalate tensions with Greece in a bid to force the downing of a Turkish jet over the Aegean, thus discrediting the government and ultimately leading to its downfall.

Seventeen retired generals and four active-duty admirals were among those detained and brought for questioning in Istanbul, say reports. Among those pictured being brought into custody include the ex-air force chief Ibrahim Firtina and the former head of the Istanbul-based First Army, Cetin Dogan, who is accused of spearheading the plot. The retired head of the navy Ozden Ornek is also among those being questioned, said Turkish media.

Under Turkish law, the authorities have 48 hours to question the suspects before they must be brought before the courts. Although officials have been keeping largely tight-lipped about the detentions, Turkish Prime Minister Recep Tayyip Erdogan confirmed the arrests on Monday during a visit to Spain.

“Sledgehammer” was first reported in January by the Taraf newspaper, which routinely targets the army.

It said the plan was discussed at a military seminar in March 2003 and published the transcripts of audio tapes that appeared to confirm that some kind of anti-government action was considered. The general staff has said the seminar involved the discussion of war-time contingency plans and denied any coup plot. Dogan has confirmed the threat of Islamist movements was discussed, but said documents were doctored to include plans to bomb two mosques and for the downing of a Turkish plane.

Retired and active-duty soldiers are already among dozens of defendants in a controversial case against a network which allegedly planned assassinations and other violence to spark political chaos and prompt a military coup.

Opponents of the AKP see it as a threat to the country’s secular system. The probe into the so-called Ergenekon network, under way since 2007, was initially hailed as a success in a country where all political groups agree military interventions in politics must stop.

But its credibility waned as police began arresting journalists, writers and academics who were known AKP critics, with prosecutors relying heavily on anonymous letters and secret witnesses.