Russia expressed a thinly veiled protest on Thursday at the grounding by Turkish authorities of a Moscow-Damascus passenger jet over accusations it was carrying "illegal cargo."

Turkish F-16 fighter jets forced down the Syrian Air Airbus A320 some three hours after it had taken off from Moscow's Vnukovo international airport. Turkey eventually permitted the A320 to resume its flight after a five-hour inspection of the aircraft that resulted in the seizure of a number of items.

"There is illegal cargo on the plane that should have been reported," Turkish Foreign Minister Ahmet Davutoglu told national media.

Turkish Prime Minister Recep Tayyip Erdogan said the intercepted plane was carrying Russian-made military gear and ammunition destined for the Syrian military.

“We are concerned that the life and security of the passengers, including 17 Russian nationals, was endangered,” Russian Foreign Ministry spokesman Alexander Lukashevich said on Thursday.

He said Turkey had not informed Russia that its nationals were on board and that Russian embassy officials and doctors had been denied access to the plane

“Russia insists on an explanation of such behavior with regard to the Russian nationals and demands that measures be taken to prevent any such incidents happening in the future,” he said.

The United States said meanwhile that it supported Turkey’s decision to force the plane down and indicated it would raise the matter with Russia.

“We strongly support the government of Turkey’s decision to inspect the plane,” State Department spokeswoman Victoria Nuland said, adding that Washington was “concerned by any effort to supply military equipment to the Assad regime.”

The episode was likely to come up in bilateral discussions between US and Russian officials, she added.

Moscow has repeatedly blocked international sanctions against the embattled regime of Syrian President Bashar al-Assad over what it says is a pro-rebel bias. Tens of thousands of people have killed been since the outbreak of civil war in Syria in March 2011, according to opposition groups.

Russia has insisted that its ongoing arms deliveries to Syria are in accordance with international law.

Syrian Ambassador to Moscow Riad Haddad was summoned to the Russian Foreign Ministry on Thursday.

Syrian Anger

Syrian authorities on Thursday demanded that Turkey returned the seized cargo.

"There were no weapons or any prohibited cargo on board," said the Syrian Foreign Ministry. “These hostile actions by the Turkish authorities are further evidence of the aggressive policy by the Turkish government."

The ministry also accused Ankara of “training terrorists, sheltering them, and sending them to Syria.”

Tensions between Turkey and Syria boiled over late last Wednesday when a mortar round apparently fired from Syria killed five civilians in the Turkish border town of Akcakale.

Turkey responded with artillery strikes against targets in violence-wracked Syria and the Turkish parliament authorized the government to order more strikes as necessary.

Although Damascus apologized for the incident, Turkish and Syrian artillery exchanged fire a number of times over the ensuing six days.

Syria responded to the grounding of the plane in Ankara by ordering its Air Force to intercept any Turkish planes in its airspace, the Lebanese newspaper Addiyar reported.

Putin Postpones Turkey Visit Until December

The potential date for a visit by Russian President Vladimir Putin to Turkey has been moved back from mid-October to the beginning of December, the Kremlin said on Thursday.

“December 3 is considered one of the possible dates for the president’s working visit to Istanbul to attend a meeting of the High-Level Cooperation Council,” president's press secretary Dmitry Peskov told reporters in Moscow.

“The final date will be agreed through diplomatic channels,” he added.

Turkish Prime Minister Recep Tayyip Erdogan visited Moscow in July and Putin had been expected to attend a meeting of the High-Level Cooperation Council in Turkey on October 15.

The announcement of the new date for the meeting comes a day after Turkish fighter jets forced a Syria-bound passenger plane with Russian citizens on board to land at the airport in Ankara so that it could be searched for military cargo. The Russian Foreign Ministry said it was "concerned" by Turkey's treatment of the Russian citizens during the incident.

The Russian Foreign Ministry has earlier said that energy issues would primarily be discussed during Putin’s visit. However, the recent developments in the Syrian crisis, including incidents on Turkey-Syria border, could also be part of the agenda.