ISTANBUL, Turkey: The interception of a passenger plane allegedly carrying military gear from Moscow to Damascus is a sign of Turkey’s mounting frustration at the drawn-out conflict and its inability to hasten regime change in Syria, according to analysts.

Recent cross-border shelling from Syria that killed five Turkish civilians near the countries’ 910-kilometer 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 [President Bashar Assad’s] 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. The war in Syria has now 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 intercepted Wednesday 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.

Mehmet Yegin, an analyst with the Ankara-based International Strategic Research Organization, said it was not yet clear whether the decision to force down the Moscow-to-Damascus plane had been 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.

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 Sergei Lavrov said Friday that the cargo contained electrical equipment for radar stations, calling it “dual-purpose” equipment that was not forbidden by any international conventions.

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 Moscow 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 was “getting really nervous” with hostilities raging near its border.

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.”