Search teams have reportedly found the boots and helmets belonging to two Turkish aviators whose plane was shot down by Syrian forces last week, but there's still no sign of the pilots themselves.

Top Turkish officials announced today the helmets were found among the two-seat Air Force plane's wreckage, Turkey's prominent Hurriyet Daily reported. No parachutes have been found but the flyers' boots were discovered days before, Turkish Prime Minister Recep Tayyip Erdogan said.

Erdogan said it was unclear whether the pilots had been able to eject before the plane went down.

But that might not have mattered, according to former fighter pilot and ABC News consultant Steve Ganyard. The plane that was hit, reportedly a reconnaissance version of the F-4 Phantom fighter, is an old but extremely fast aircraft, capable of flying at over twice the speed of sound. Ganyard said that even if the pilots managed to eject, it would've been difficult for them to survive the ejection alone and it's possible the sheer wind blast could have ripped the helmet and boots from them. If the pilots were unable to eject, Ganyard said, a plane as fast as the Phantom could have hit the water "as if it were concrete" - spreading debris wide and leaving little intact.

Still, the search continues.

In addition to the mystery of what happened to the pilots, Turkey and Syria continue to disagree about what led to the shoot down in the first place. In a letter written to the United Nations early this week, the Turkish government claimed the unarmed plane had been flying in international airspace when it suddenly came under fire from Syrian air defenses. After being hit, the plane turned and entered Syrian airspace before crashing, the letter said.

But a day before that letter was sent, a top Syrian official told the Syrian State News Agency that the plane had "blatantly" violated Syrian airspace and the shooting was a defensive and sovereign act.Jihad Makdessi, a spokesperson for Syria's Foreign and Expatriates Ministry, said the jet had gone deep into Syrian airspace before it triggered an automatic air defense system.

The incident prompted a stern warning from the Turkish government about future military action and NATO condemnation, but the father of one of the pilots urged restraint from his leaders.

"It is not appropriate to go to war over a pilot, an airplane or 50 airplanes," Ali Erton, father of missing pilot Capt. Gokhan Ertan, told a Turkish television station. "What matters is that my son serves his country… I am a man of faith and do not believe martyrs ever die."

Turkey branded its former ally Syria "a clear and imminent threat," on Tuesday as its Prime Minister Recep Tayyip Erdogan vented his fury over the downing of a Turkish fighter jet.

In his most outspoken criticism of the Damascus regime, Erdogan vowed to retaliate against the "heinous act" and promised a change of military attitude to any Syrian officer approaching the common border.

"The rules of engagement of the Turkish Armed Forces have changed given this new development," Prime Minister Recep Tayyip Erdogan told parliament following the shooting down of F-4 Phantom jet Friday. The two pilots are still missing.

Any risk posed by Syria on the Turkish border will be "considered a threat and treated as a military target," he said in a jam-packed room of lawmakers who frequently interrupted the address with applause.

Erdogan said his government would retaliate "with determination" and take what he called the "necessary steps by determining the time, place and method by itself".

The prime minister said Turkey's military jet violated the Syrian airspace for a short time and "by mistake" and repeated that it was unarmed, flying solo when it was shot down by Syria "without a single warning."

"We did not receive a single warning, note from Syria (regarding airspace violation)...They acted without warning. This is a hostile act," Erdogan said.

Erdogan said that Turkish airspace had been violated 114 times by military aircraft from different countries, including Syria, since January 1, 2012.

"Syrian helicopters violated our airspace five times. These were short-term violations," to which Turkey issued the necessary warnings, Erdogan noted.

"This latest development shows that the Assad regime has become a clear and imminent threat to the security of Turkey, as well as for its own people," he added.

Erdogan broke with former friend and ally Assad, whom he called "a bloody dictator," after unrest that erupted mid-March last year met a bloody response from Damascus, sending more than 33,000 refugees into Turkey.

"Turkey will support Syrian people in every way until they get rid of the bloody dictator and his gang," he said on Tuesday.