Turkey’s forcing down of a Syrian passenger jet en route from Moscow to Damascus has heightened tensions between the two countries and provoked a sharp protest from the Russian government.

The incident, which took place late Wednesday, underscores the danger of the US-backed drive to topple the regime of Bashar al-Assad in Syria by means of a sectarian civil war spilling over to a far wider regional war.

The Syrian government condemned Turkey’s action as an act of “air piracy.” SANA, the state news agency, quoted Syrian Arab Airlines Director Ghaida Abdulatif, who charged Turkish authorities with violating international law by forcing down the Syrian Airbus A-320 plane. He added that the close approach of two Turkish F16 fighter planes had nearly caused a midair collision.

She also charged that Turkish security forces had assaulted members of the Syrian aircraft’s crew. This was confirmed by the plane’s flight engineer, Jasem Kaser, at a press conference in Damascus.

Kaser showed reporters his badly bruised arm and recounted that Turkish soldiers had pointed their guns at the crew members, handcuffed them, and forced them to lie on the tarmac after they demanded that the Turks produce a warrant to search the plane’s cargo. They were further manhandled as Turkish officials tried to force crew members to sign declarations that the plane had made an emergency landing.

Russia issued a formal protest over the incident, charging that the lives of the 35 passengers, 17 of whom were Russian, had been placed at risk. Moscow also protested that Russian embassy officials, who had gone to the airport with a doctor, were denied the right to speak to the passengers.

The passengers were detained onboard the plane for eight hours without any explanation. They were provided no food.

On Thursday evening, Prime Minister Recep Tayyip Erdogan justified Turkey’s action in forcing the Syrian plane to land in Ankara on the grounds that the aircraft was transporting “equipment and ammunition shipped to the Syrian Defense Ministry” from a Russian military supplier.

Syria’s Foreign Ministry responded that Erdogan was “lying… to justify his government’s hostile attitude towards Syria,” while Russian Foreign Minister Sergei Lavrov told reporters on Friday that there were “no weapons” on the plane.

“We have no secrets,” said Lavrov. “There were, of course, no weapons on the plane and could not have been any. There was a cargo on the plane that a legal Russian supplier was sending in a legal way to a legal customer.”

Lavrov clarified that the 12 containers confiscated from the plane by Turkish authorities held radar components that served a “dual purpose,” meaning that they could have either a civilian or military use.

Such materials, Russian officials pointed out, require no special declarations as they pose no danger to passengers or crew members, and their transport to Syria on the passenger jet was in violation of no international laws.

While claiming to have intercepted arms and ammunition bound for Syria, the Turkish government has made no move to publicly display these materials, which it almost certainly would if they existed. A Turkish Foreign Ministry official told the daily Hürriyet Thursday, “We are not prepared to comment on the description of the cargo. We will discuss it after we finish examining it.”

Within hours of the plane being forced down in Ankara, Turkish Foreign Minister Ahmet Davuto&;lu told the media, “We are determined not to allow arms supply via Turkish airspace to a regime that is resorting to cruelty against its own people. Trying to do so by using our airspace is unacceptable.”

Radar components are hardly arms that can be used against the Syrian people. They are, however, key to Syria’s self defense against a Turkish or US-NATO air war along the lines of the one waged against Libya last year. One thing that distinguishes the two countries is Syria’s Russian-supplied air defense system, which is one of the most sophisticated in the Middle East.

Turkey has already begun massing warplanes against Syria, sending 25 F16s to a base near the border. On Friday, it scrambled two F16 fighters in response to a Syrian military helicopter that flew over the Syrian border town of Azmarin, where there has been intense fighting between government forces and Western-backed “rebels.”

The Turkish action was aimed at pressuring Moscow to stop providing air defense material to Syria, according to a Russian analyst quoted by RIA Novosti. “This was obviously a demonstrative step. This is clearly an element of pressure on Russia,” said Vladimir Yevseyev, director of the Russian Center for Socio-Political Studies.

“Turkey has a strong prejudice that the crash of the Turkish airplane [a Turkish warplane shot down on June 22 after it had invaded Syrian airspace] was organized with the help of Russian weapons… Supplies of Russian weapons curb to a large extent the aggressiveness of certain circles in Turkey towards Syria. And this is a serious problem,” Yevseyev added.

Russian President Vladimir Putin canceled a planned visit to Turkey in the wake of the Syrian plane being forced down. He had been scheduled to go to Ankara on October 14 for talks with Erdogan centering on Syria and Russian-Turkish trade, which is expected to reach $35 billion this year. The Russian daily Vedomosti quoted unnamed Kremlin sources as saying that Putin feared visiting only one of the antagonists in the escalating Turkish-Syrian conflict could be “misinterpreted.”

RIA Novosti quoted an unnamed source in one of Russia’s security agencies as saying Moscow suspects that Turkey’s provocative action may have been instigated by Washington. Intelligence about the plane’s cargo, he said, would likely come from American interception and decryption of communications between Moscow and Damascus. “The Turkish special service simply does not have any other resources,” he said.

The Turkish provocation against the Syrian passenger plane unfolded under conditions in which the two countries are on the brink of war, with Turkey repeatedly firing artillery barrages into Syria in response to stray shells from the fighting between Syrian government forces and the “rebels” along the border. One such shell hit a residential home in the Turkish border town of Akçakale on October 3, killing five people and prompting Turkish military retaliation.

The shells from the Syrian side of the border may well have been fired by the so-called “rebels” with the intention of provoking Turkish intervention. If so, the shells themselves were probably supplied by the Turkish government, which, together with the US, Saudi Arabia and Qatar, is arming, training and supporting the militias seeking to overthrow Assad.

Turkish officials Friday denied media reports that US and French Special Forces troops have been deployed in Turkey near the Syrian border to train and supply the “rebels.”

“American and French special forces have been at Incirlik airbase in southern Turkey for weeks, according to security sources,” the Times of London reported on Thursday. “Since early summer, the NATO base has been a nerve-centre for Western nations and regional allies. Agents for Saudi Arabia and Qatar are also at the site, working to channel weapons and cash to the rebels.”

The report comes just days after the New York Times revealed that the Pentagon has set up a base in Jordan, just 35 miles from the Syrian border, staffed by over 150 war “planners,” most of them Special Forces.

Like their Turkish counterparts, the Jordanian authorities denied that there was any truth to this report, only to have it confirmed by the Pentagon and US Defense Secretary Leon Panetta.