The interception of a Syrian passenger plane from Russia, allegedly carrying military gear to Damascus, is a sign of Turkey's mounting frustration at the drawn-out conflict and its inability to hasten regime change in its neighbor, according to analysts.
Recent cross-border shelling from Syria that killed five Turkish civilians near the countries' 910-kilometer (566-mile) common frontier may have forced Turkey to act, but its options were limited.
"There's nothing magical about the timing. It's a coincidence resulting from the build-up of frustration in Ankara," said Fadi Hakura, a Turkey analyst at the Chatham House think tank in London. "Turkey wants to hasten the demise of the Assad regime in Damascus, but really its hands are tied."
Turkish Prime Minister Recep Tayyip Erdogan has been at the forefront of international efforts to put pressure on the Assad regime and end its 19-month crackdown on the opposition. Last year, Ankara began allowing members of the rebel Free Syrian Army to operate in Turkey and now Syria's civil war has reached a stalemate.
"Given the current international impasse over the conflict in Syria, practical measures such as the interception of aircraft will become increasingly important for states seeking to restrict Syrian government forces' access to military-related goods from external sources," said Edin Omanovic, a researcher with the Stockholm International Peace Research Institute.
Turkish fighter jets on Wednesday intercepted the Syrian Air plane they said was carrying Russian ammunition and military equipment destined for the Syrian Defense Ministry. Syria branded the incident piracy and Russia said the action endangered the lives of Russian citizens aboard the aircraft.
Russia has been one of Syria's main weapons suppliers, and it has also been shielding the regime of Syrian President Bashar Assad from U.N. sanctions.
Mehmet Yegin, an analyst with the Ankara-based International Strategic Research Organization, said that it was not yet clear whether the decision to force down the Moscow to Damascus plane was part of a larger drive to change the dynamic of the war.
"If it is acting with its allies, it's a clear message to Russia to get out of the picture and stop arming Syria," he added. "It is such a bold move, that one wonders if Turkey acted alone."
U.S. State Department spokeswoman Victoria Nuland declined Thursday to comment on Turkish media reports that the intelligence on the plane's contents had come from the United States.
But she told reporters that Washington backed Turkey's decision to intercept the plane.
"Any transfer of any military equipment to the Syrian regime at this time is very concerning, and we look forward to hearing more from the Turkish side when they get to the bottom of what they found," said Nuland.
The exact contents of the cargo are still unclear: Turkey's prime minister described it as "ammunition," while Yeni Safak, a newspaper close to the Turkish government, reported Friday that the cargo contained 12 pieces of missile parts and "trigger devices" and that intelligence received was that it could be used by Syria against Turkey.
Russian Foreign Minister Sergey Lavrov said late Friday that the plane was carrying radar parts for Syria, that the shipment complied with international law and that there was no weapon on board.
Lavrov said, however, that the cargo, consisting of "electric equipment for radars," was of dual purpose and could have civilian and military applications. The Russian company that sent it demands its return, he said.
Earlier, the respected Russian daily Kommersant quoted an unidentified source saying there were 12 boxes of spare parts for radars of the Syrian missile defense units.
"If the Kommersant report is right, you could speculate about this being part of a build-up to imposing a no-fly zone," said Hugh Pope, who leads the Turkey program for the International Crisis Group.
Such a move could be the first step toward lending Syria's rebels the same kind of international air support that helped bring down Libya's Muammar Gadhafi last year.
But most analysts see no push — either in Turkey or among its Western allies — for outside military involvement in Syria.
Fyodor Lukyanov, editor-in-chief of Russia in Global Affairs, said the incident also wasn't about sending any messages to Russia in particular, because Russia's stance on Syria is already clear and isn't likely to change.
Lukyanov said the plane incident showed that Turkey is "getting really nervous" with hostilities raging near its border. "Turkey is trying to demonstrate how tough and capable it is."
Meanwhile, Russia's and Turkey's growing business ties could suffer, he said.
If Turkey keeps on getting involved in Syria, "the political situation in Syria will have an increasing influence on other areas of their (Russian-Turkish) relations," said Lukyanov. "No one wants to heat this up, but sometimes things get out of hand."
Suzan Fraser in Ankara, Turkey, and Nataliya Vasilyeva in Moscow contributed to this report.