Russian anger at Turkey over Syria plane interception
Moscow has accused Turkey of putting the lives of Russian passengers in danger by using its military to force a Syria-bound plane to land in Ankara.
The Syrian Air plane, from Moscow, was intercepted and searched on Wednesday on suspicion it was carrying weapons.
Officials in both Russia and Syria have strongly denied the allegations, with Damascus accusing Turkey of "piracy" and violating international law.
The incident has increased already high tensions between Turkey and Syria.
Shelling from within Syria killed five Turkish civilians last week - in response, Turkey fired into Syria for the first time since the uprising against President Bashar al-Assad began last year.
Meanwhile, Syria's Sana state news agency has reported an attack on a bus close to its border with Lebanon. It said eight passengers had been killed and eight injured when "terrorists" opened fire on the bus.
Shortly before the plane was grounded, Russian President Vladimir Putin had postponed a visit to Turkey, scheduled for next week, citing a heavy workload. The visit will now take place on 3 December, said Turkey.
The Airbus A320 airliner with about 30 passengers on board was intercepted on Wednesday evening by two Turkish fighters and escorted to the capital's Esenboga airport.
Turkey's Foreign Minister Ahmet Davutoglu told the Anatolia news agency that illegal and "objectionable" cargo which "should have been reported" was found during a search and confiscated.
He did not specify whether any weapons had been found, but unconfirmed reports in Turkish media said the seized items included boxes of military communication equipment.
But Russia's foreign ministry spokesman Alexander Lukashevich said Turkish officials had failed to inform Moscow that Russian citizens were on the plane.
"We are concerned that this emergency situation put at risk the lives and safety of passengers, who included 17 Russian citizens," he said.
"The Russian side continues to insist on an explanation of the reasons for such actions by the Turkish authorities."
The plane was allowed to take off at 02:30 (23:30 GMT on Wednesday), after several hours on the ground.
Turkey's foreign ministry said there was "no basis" for Moscow's safety concerns.
"After the landing, all measures were taken to ensure the safety of all passengers and to cater to their possible needs," the ministry said.
In a statement quoted by AFP, it said the pilot had been asked to turn back while over the Black Sea, before entering Turkish airspace.
Syrian Transport Minister Mahmoud Saeed accused Turkey of carrying out "air piracy" and breaking civil aviation agreements, according to Lebanon's al-Manar TV.
Gaida Abdul Latif, the head of Syrian Air, said the Turkish military aircraft "forced the plane to land without giving prior warning to the pilot".
"The military aircraft were so close that there could have been an accident," she said.
Meanwhile the plane's flight engineer, Haitham Kasser, said he witnessed the search, and that the crew had not objected to Turkish officials' requests to remove some of the cargo.
But when the crew refused to hand over the boxes in question without a receipt, the officials returned with members of the armed forces, he said.
"They handcuffed us and made us lie on the ground, then they took us out of the plane in two vehicles," he told the Associated Press within Syria.
Mr Davutoglu said Turkey remained determined to stop any transfer of weapons to Syria through its airspace.
In another sign of deteriorating relations, Turkish officials revealed on Thursday that Syria had stopped buying electricity from its neighbour last week.
US Senator John McCain has meanwhile said the US should intervene in Syria, to help create safe zones and get arms and support to the anti-Assad rebels.
The countries in the region were "crying out for American leadership" on Syria, he told the BBC, but he dismissed the idea of sending US troops into Syria.
On Wednesday, the US confirmed that it had a military task force working in Jordan, helping to plan for a potential regional escalation of the Syrian conflict and in monitoring the security of Syria's chemical and biological weapons.