Syria has said Turkish civilian flights are banned from flying over its territory after a similar move by Turkey on Syrian flights, as relations between the former allies continue to plunge to new depths.
A Syrian foreign ministry statement, carried by the state news agency SANA, said the ban would take effect on Sunday.
The decision, "in accordance with the principle of reciprocity", was in retaliation for Turkey's move to stop Syrian civil aviation flights over its territory, SANA said.
The announcement came after Ahmet Davutoglu, Turkey foreign minister, said: "Yesterday we closed our airspace to Syrian civilian flights as we have previously done for Syrian military flights."
In-depth coverage of escalating violence across Syria
Ties between Turkey and Syria took a sharp turn for the worse when they engaged in sporadic cross-border shelling last week.
Turkey intercepted on Wednesday a Syrian passenger jet carrying what it said were Russian-made munitions for the Syrian army.
Syria has denounced the interception as air piracy, while Russia said the cargo was radar parts that complied with international law.
Turkey has not yet announced a similar ban but said it will ground Syrian civilian aircraft again if it suspects they are carrying military equipment for the forces of Syrian President Bashar al-Assad.
Davutoglu, held talks with Arab and European leaders in Istanbul on Saturday. He met Guido Westerwelle, German foreign minister, before the pair met Abdelbaset Sieda, the head of the Syrian National Council opposition group.
"The Syrian government is trying to export the crisis to the neighbouring countries so that the pressure on them will lessen," Sieda said.
Davutoglu also met Lakhdar Brahimi, the UN envoy to Syria, and Nabil Elaraby, the Arab League chief.
Brahimi was in Iranian capital, Tehran, on Sunday for talks with Ali Akbar Salehi, Iran's foreign minister, who handed him a proposal aimed at ending the conflict.
Salehi said Iran had "handed its unofficial detailed proposal in writing aimed at solving the Syrian crisis" to Brahimi as well as Egypt, Saudi Arabia and Turkey, in comments broadcast on Arabic-language al-Alam television.
He did not go into details about the proposals, only adding Tehran would support efforts by the international envoy.
Brahimi welcomed the Iranian initiative and is due to meet Saeed Jalili, Iran's top security official, on Monday before leaving for Baghdad later that day, the website of state television reported.
Brahimi is on a regional tour aimed at finding a solution to the conflict in Syria after Damascus rejected a UN call to implement a unilateral ceasefire.
At a joint news conference with Westerwelle on Saturday, Davutoglu said Turkey was prepared to use force again if it was attacked, just as it did last week when a shell fired across the border from Syria killed five Turkish villagers.
SANA reported that Syrian government officials and Russia's ambassador in Damascus discussed ways to establish a joint Syrian-Turkish security committee that would "control the security situation on both sides of the border in the framework of respecting the national sovereignty of the two countries".
Turkey has made no comment on the proposal, and it is unclear whether Russia has presented it to the Turkish government yet.
Sieda said that "instead of suggesting a dialogue between Turkey and Syria, Russia should pressure the Assad regime they have been supporting and prevent them from massacring its own people as well as ceasing arms shipment to Syria".
Rallies in Lebanon
In another Syria-related development, hundreds of people took to the streets of Beirut in neighbouring Lebanon on Sunday for two separate rallies, one expressing support for the Assad regime and the other calling for its downfall.
Demonstrators held posters bearing slogans including "Thank you Russia!" and "Lebanon forever with Assad's Syria," and also chanted slogans against Saudi Arabia and Qatar, which support the revolt against the regime.
They also waved flags of Syria, Iran and the Lebanese group Hezbollah, which supports Assad.
Since the anti-regime uprising broke out in Syria in March last year, Russia and China have vetoed three draft UN Security Council resolutions aimed at pressuring Assad's regime.
Later, in the heart of Beirut, hundreds of supporters of a radical Sunni Muslim leader, Sheikh Ahmed al-Assir, gathered for a protest held for "our brothers in Syria".
The participants waved Syrian independence flags in support for the ongoing revolt.
Syria dominated Lebanon politically and militarily for three decades, and the small Mediterranean country is deeply divided over the conflict in its neighbour.