Turkey and Syria said their navies were jointly searching on Saturday for Turkish airmen shot down by Syria over the Mediterranean, while nearby Turkish authorities were hosting thousands of rebels fighting President Bashar al-Assad.
Signals from both sides suggested neither wanted a military confrontation over Friday's shooting down of the jet near sea borders of both states. However, the joint operation will clearly sit uneasily with both forces, given the bitter hostility between the two former allies over Assad's 16-month crackdown on opponents.
Turkey has promised to respond decisively.
"It is not possible to cover over a thing like this. Whatever is necessary will no doubt be done," Turkish President Abdullah Gul told reporters, adding that Ankara had been in telephone contact with Syrian authorities.
The incident, whatever its causes, demonstrated Syria's formidable Russian-supplied air defences - one of the many reasons for Western qualms about any military intervention to halt bloodshed in the country.
Turkey's Deputy Prime Minister Bulent Arinc said the downed jet was not a warplane but a reconnaissance aircraft, state television TRT reported. Turkish media had earlier identified it as an F-4 Phantom, a fighter also used for reconnaissance
Gul said it was routine for fast-flying jets to cross borders for a short distance and that an investigation would determine if the aircraft was brought down in Turkish airspace.
Syria's military said the Turkish plane was flying low, just one kilometre off the Syrian coast, when it was shot down. It had been tracked at first as an unidentified aircraft and its Turkish origine established subsequently.
"The navies of the two countries have established contact. Syrian naval vessels are participating along with the Turkish side in the search operation for the missing pilots," it said.
With the second biggest army in NATO, a force hardened by nearly 30 years of fighting Kurdish rebels, Turkey would be a formidable foe for a Syrian military already struggling to put down a popular uprising and an increasingly potent insurgency.
"Playing with fire"
Turkish Foreign Minister Ahmet Davutoglu met Turkey's military commanders and intelligence chief to discuss the search for the pilots and Ankara's next steps.
The meeting followed an emergency security session chaired by Prime Minister Tayyip Erdogan on Friday evening.
"Turkey will present its final stance after the incident has been fully brought to light and decisively take the necessary steps," said a statement from Erdogan's office.
Turkish newspapers were less restrained.
"They (the Syrians) will pay the price," said Vatan, while Hurriyet daily said: "He (Assad) is playing with fire."
The joint Syrian-Turkish naval operation was not without its tense ironies. Less than 50 Km (30 miles)away in Turkey's southeastern Hatay province, authorities are giving refuge to the rebel Free Syrian Army who mount daily attacks on Syrian government forces.
Saudi Arabia and Qatar are paying salaries to Syrian rebels, with Turkish involvement, an Arab diplomat in Jeddah said.
"The payment has been going on for months and the agreement was made on April 2 by Saudi Arabia and Qatar, with logistical organisation from Turkey where some Free Syrian Army factions are based," he said, asking not to be named.
"The point of this is to encourage as many factions of the Syrian army to defect and to organise the FSA, control it and prevent any extremist organisations from joining it."
A spokesman for Saudi Arabia's foreign ministry said he was not aware of reports that the kingdom was funding Syrian rebels.
The souring of Syrian-Turkish relations has provoked concern among Turks that Syria may revive its former support for Kurdistan Workers Party (PKK) insurgents in southeastern Turkey.
"It's possible the Turks were sending jets in the area in response to an apparent escalation of the PKK's activities," Hilal Khashan, political science professor at the American University of Beirut, told Reuters. "Turkey may suspect that Syria and Iran are supporting Kurdish rebel activities now as a reaction to Turkish support of the Syrian revolt."
However, Khashan said he did not expect a harsh military reaction from Turkey. "It is under a tight leash by the United States. They don't want to start a war tomorrow."
Budding civil war
A civil war, or something closely resembling one, is already in full swing in Syria, where fighting or shelling engulfed parts of the cities of Aleppo, Hama, Homs, Deir al-Zor and Douma, according to the Syrian Observatory for Human Rights.
The British-based watchdog also reported fierce clashes and shelling in the town of al-Bab in Aleppo province, where army helicopters were flying overhead. It said rockets and gunfire had killed three people in al-Qusair, a town in Homs province. Two men were killed in an ambush by security forces in Hama.
Syrian army shelling killed at least 28 people in Deir al-Zor, opposition activists said. A hospital source said three women and several children were among civilians killed when shells hit their homes in the Old Airport area.
The International Committee of the Red Cross (ICRC) said it was still negotiating access to hundreds of trapped civilians and wounded people in Homs after a failed attempt to reach them on Thursday. "We are still in discussions to try to enter the (old) city," ICRC spokesman Jean-Yves Clemenzo said in Geneva.
Turkey fears the fighting, much of which pits majority Sunni Muslim dissidents and rebels against Assad's Alawite-dominated security forces, could unleash a flood of refugees over its own border and ignite a regional sectarian conflict.
It already hosts 32,000 Syrian refugees near the border. The opposition Syrian National Council meets in Istanbul.
Ankara has previously floated the possibility of setting up some kind of safe haven or humanitarian corridor inside Syria, which would entail military intervention, but has said it would undertake no such action without U.N. Security Council approval.
Turkey has said however that Assad must go.
It was unclear why the Syrians had shot down the aircraft, which, having left a base in Malatya, was flying close to a corridor linking Turkey with Turkish forces on Northern Cyprus.
"The Syrian military may have taken a calculated gamble by downing the Turkish plane, which could boost the morale of Assad's loyalists after increased defections from the military," said Yasser Saadeldine, an opposition Syrian commentator.
"A Turkish retaliation would fit into the fantasy he (Assad) is peddling that the uprising is a foreign conspiracy."
It was also possible the air defences could have mistaken the aircraft for a defecting pilot, following an incident earlier in the week when a Syrian aircraft landed in Jordan.
Russia and China, Assad's strongest backers abroad, firmly oppose any outside interference in the Syrian crisis, including foreign arming or funding of insurgents, saying envoy Kofi Annan's stalled peace plan is the only way forward.
Assad's prime minister, appointed after a parliamentary election conducted last month despite the violence convulsing the country, named a new cabinet on Saturday.