ANKARA, Turkey (AP) — Escalating tensions with Russia, Turkey defended its forced landing of a Syrian passenger jet en route from Moscow to Damascus, saying Thursday it was carrying Russian ammunition and military equipment destined for the Syrian Defense Ministry.

Syria branded the incident piracy and Russia called the search illegal, saying it endangered the lives of Russian citizens aboard the plane.

The accusation by Turkish Prime Minister Recep Tayyip Erdogan contradicted denials by both Russia and Syria that anything illegal had been aboard the Airbus A320 that was intercepted over Turkish airspace late Wednesday.

"Equipment and ammunitions that were being sent from a Russian agency ... to the Syrian Defense Ministry," were confiscated from the jetliner, Erdogan told reporters in Ankara. "Their examination is continuing and the necessary (action) will follow."

He did not provide details, but Turkish media said the seized cargo included missile parts as well as radio receivers, antennas and other military communications equipment.

"As you know, defense industry equipment or weapons, ammunitions ... cannot be carried on passenger planes," Erdogan said. "It is against international rules for such things to pass through our air space."

Erdogan refused to say how — or from whom — Turkey had learned that the twice-weekly scheduled flight would be used to transport military gear to Syria.

"As you will appreciate, those who gave the tip, which establishments, these things cannot be disclosed," he said.

The United States said it 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 State Department spokeswoman Victoria Nuland.

She declined to comment on Turkish reports that the intelligence on the plane's contents had come from the United States. The plane was allowed to continue to Damascus after several hours, without the cargo.

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Turkish-Syrian relations have plummeted over the conflict in Syria, which has expanded into a civil war that threatens the stability of the Middle East. Syrian opposition activists estimate more than 32,000 people have been killed since March 2011, when the uprising against President Bashar Assad's regime began.

Turkey has called for Assad to step down, while Damascus accuses Turkey of supporting the rebels. The two neighbors have traded artillery fire over Syria's northern border throughout the past week.

Hours before Erdogan's statement, Russian Ambassador Vladimir Ivanovsky held talks with Turkish officials at the Foreign Ministry.

In Moscow, Russian Foreign Ministry spokesman Alexander Lukashevich said the Kremlin was concerned that the lives and safety of the 35 passengers, including 17 Russian citizens, had been endangered.

"The Russian side continues to insist on an explanation for the Turkish authorities' actions toward Russian citizens and on the adoption of measures to avoid such incidents in the future," Lukashevich said in a statement.

Turkey's Foreign Ministry said the pilot of the Syrian Air jetliner had been warned of Turkey's intention to ground it as he approached from the Black Sea and he was given the opportunity to turn back, but declined.

Rejecting claims that passengers were ill-treated, the ministry said those on board were allowed to leave the plane if they wanted and that there was a medical crew and ambulances on standby. It also said the pilot did not provide a passenger list and therefore Turkish officials did not know there were Russians on board until after the plane landed.

Separately, the Foreign Ministry said it had submitted a formal protest note to Syria for the violation of civil aviation rules and declared Syrian air space unsafe for Turkish planes.

In Damascus, Syrian Foreign Ministry spokesman Jihad Makdessi rejected the Turkish accusations as "absolutely untrue," saying the plane was not carrying ammunition or any illegal cargo. Turkey's decision to force the plane to land amounted to piracy, said Transportation Minister Mohammad Ibrahim Said.

The general manager of the Syrian Civil Aviation Agency also blasted Turkey's forced landing of the plane, calling it "contrary to regulations and aviation norms."

The plane's pilots were not asked to land but were surprised by the Turkish F-16 fighter jets that intercepted the flight, the official, Ghaidaa Abdul-Latif, told reporters in Damascus.

A Syrian Air engineer who was aboard, Haithan Kasser, said armed Turkish officials entered the plane and handcuffed the crew before inspecting packages that he said contained electrical equipment.

The Moscow airport that cleared the Syrian plane for takeoff denied it carried any forbidden cargo.

"No objects whose transportation would have been forbidden under aviation regulations were on board," said Vnukovo Airport spokeswoman Yelena Krylova, ITAR-Tass reported. She said all documentation was in order, though she would not say who sent the cargo.

Meanwhile, family and supporters of two journalists believed to be detained in Syria appealed in Istanbul for their release. Arzu Kadoumi said her husband Bashar Fahmi, a reporter for Al-Hurra network, and his Turkish cameraman, Cuneyt Unal, had been missing for 53 days.

Inside Syria, battles continued in the southern Idlib province that abuts the Turkish border as rebels sought to consolidate control of a strategic town on the country's main north-south highway. Rebels said they captured Maaret al-Numan on Wednesday.

The Britain-based Syrian Observatory for Human Rights said clashes continued Thursday after rebels attacked a military convoy and nearby army checkpoints. The fighting killed more than a dozen people, the Observatory said.

The Observatory also said eight people were killed and another eight wounded when unknown gunmen fired on their bus near the coastal city of Tartous. Syria's state news agency SANA said the men were Syrian workers returning from Lebanon.

In the southern province of Daraa, gunmen shot dead the brother of a member of Syria's parliament while raiding his home, the Observatory and SANA said. The parliament member, Khalid al-Abboud, regularly defends the Syrian regime on TV.

The Observatory said gunmen also killed the son of another legislator, Mohammed Kheir al-Mashi, at his home in Idlib province.

The activist claims could not be independently verified because of restrictions on reporting in Syria.

Meanwhile, state-run Syrian TV reported an explosion in the capital Thursday night near the Ministry of Education and the Military Court. A Syrian official said the blast wounded two people.

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Jordans reported from Istanbul. Associated Press reporters Matthew Lee in Washington, Albert Aji in Damascus, and Nataliya Vasilyeva and Max Seddon in Moscow contributed to this report.