Prime Minister Ahmet Davutoglu told reporters that "those coming from Syria can go back to join the fight" for Kobane, but that Turkish and other nationals would not be allowed to cross the border.
Kurdish fighters are seeking to hold back the advance by Islamic State (IS) jihadists to take Kobane and Turkey is coming under increasing pressure to allow Kurdish reinforcements to cross the nearby border.
"We don't let Turkish citizens go into Syria because we don't want them to be a part of the conflict in Syria. We are trying to stop those who are attempting to do so illegally. It is against the laws in a constitutional state," he said.
Turkey has been wary of letting Turkish Kurds cross the border to join the fight for Kobane, fearing the creation of a potent Kurdish fighting force straddling the Turkish-Syrian borders.
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The Turkish security forces have waged a 30-year conflict with the outlawed Kurdistan Workers Party (PKK) which has links to the main Syrian Kurdish Party the Democratic Union Party (PYD).
Davutoglu's comments come after French President Francois Hollande on Tuesday said Turkey "must absolutely open its border" to allow reinforcements to reach Kobane.
UN envoy Staffan de Mistura last week called on Turkey to allow volunteers and their equipment to be able to enter Kobane to contribute to its defence.
"It's easy to talk from Paris. Do they know what's happening on the ground?" snapped Davutoglu, pointing to how Turkey was hosting some 200,000 refugees from the Kobane region.