Turkey jailed over two dozen generals, including a former air force chief, on suspicion of planning the coup against President Recep Tayyip Erdogan, as Ankara Tuesday stepped up a relentless crackdown despite international concern.

Erdogan has denounced the coup, which left more than 300 dead on all sides, as a treacherous bid to oust him from power devised from the Pennsylvania compound of his arch-enemy, the US-based preacher Fethullah Gulen.

Turkish police on Monday detained seven soldiers after searching a key air base in southern Turkey used by the United States for air raids on the Islamic State group, the state-run Anadolu news agency reported.

Authorities had previously detained a senior air force general and a dozen other suspects at the Incirlik air base close to Syria who were accused of backing the failed coup, officials said at the weekend.

Turkish Prime Minister Binali Yildirim on Monday said his government cannot remain indifferent to demands for reinstating the death penalty to punish coup plotters but added that the issue must be deliberated in parliament.

Turkey launched fresh raids and sacked almost 9,000 officials Monday in a relentless crackdown against suspects behind an attempted coup that left over 300 people dead, as Western allies warned against reinstating the death penalty.

Russia's foreign ministry warned Saturday that the coup attempt in Turkey increases the threat to stability in the region.

Turkish authorities have placed seven more suspects under arrest over the triple suicide bombings at Istanbul's main airport last month, bringing to 37 the number charged over the attack, media reports said Monday.

Seven people, including children, were killed and eight others injured when a Turkish military helicopter crashed Tuesday, apparently in fog, in the northeastern province of Giresun, the army announced

Seventeen people including 11 Russians have been charged over the Istanbul airport attack, Dogan news agency reported Tuesday, bringing to 30 the total number charged over the suicide assault.

Two suspected Islamic State jihadists have been detained at Istanbul's Ataturk airport days after it was hit by suicide bombers, as Turkish authorities move to boost security at sensitive sites.

Saida Bayoudh's only son joined the Islamic State group and her husband flew to Turkey to bring him home but instead returned alone to be buried Friday as a victim of the Istanbul airport attack.