Turkey will treat any Syrian military units which approach its border as a threat and a military target, Prime Minister Tayyip Erdogan said on Tuesday.
Erdogan also said Turkey was totally in the right over Syria's shooting down of a Turkish plane and that Ankara's rational response to the incident should not be mistaken for weakness.
"Everybody should know that Turkey's wrath is just as strong and devastating," Erdogan said in a speech to his ruling AK Party deputies in parliament.
The army's rules of engagement along the two countries' border had now changed, he said.
"Every military element approaching Turkey from the Syrian border and representing a security risk and danger will be assessed as a military threat and will be treated as a military target," he said.
Turkey has demanded backing from its Nato allies over the shoot down and has called a meeting in Brussels under Article 4 of the alliance's charter, which provides for consultations when a member state feels its territorial integrity or security is under threat.
Turkey has rejected assertions from Damascus that its forces had no option but to fire on the F-4 jet as it flew over Syrian waters close to the coast on Friday and has branded the shooting an "act of aggression".
It says the aircraft was an unarmed reconnaissance plane flying over international waters.
Meanwhile, Nato condemned Syria's downing of a Turkish jet as "unnacceptable" and expressed "strong support and solidarity" with Turkey after emergency consultations Tuesday.
"We consider this act to be unacceptable and condemn it in the strongest terms," said NATO chief Anders Fogh Rasmussen. "Allies have expressed their strong support and solidarity with Turkey."
"As far as future events are concerned ... we will remain seized," he added.
However, Rasmussen appeared to play down fears of a flare-up between the two neighbours.
"It's my clear expectation that the situation won't continue to escalate," he said in response to a question.
He underlined that there was no discussion of Article 5 of NATO's founding treaty, the provision enabling the alliance to fly to the rescue of one of its partners.
Rasmussen spoke after the North Atlantic Council met for consultations on a request from Turkey following the loss of a Phantom 4 fighter jet shot down Friday by Syria. The two-man crew remain missing.
"It is another example of the Syrian authorities' disregard for international norms, peace and security, and human life," Rasmussen told a news conference.
"We continue to follow the situation closely and with great concern," he added after talks lasting a little over an hour gathering ambassadors of the 28-nation Atlantic alliance to hear Turkey's representative outline the circumstances of the incident.
"Let me make this clear. The security of the alliance is indivisible. We stand together with Turkey in the spirit of strong solidarity," Rasmussen said.
Turkey requested consultations with its allies under Article 4 of Nato's founding treaty, enabling any one of them to call for talks should they consider their territorial integrity, political independence or security under threat.
It is only the second time since the North Atlantic Treaty Organisation was set up in 1949 that consultations have been requested under that article, the last time in 2003 also being on a request from Turkey during the Iraqi war.
Asked what Nato might do should there be an escalation of tension between Turkey and Syria, the alliance chief said: "What we've seen is a completely unacceptable act and I would expect Syria to avoid such steps in the future."