Turkish Prime Minister Tayyip Erdogan addresses the audience after receiving his honorary doctorate degree from Yildiz Technical University in Istanbul October 5, 2012.  [Photo/Agencies]

ISTANBUL/BEIRUT - Turkish Prime Minister Tayyip Erdogan warned on Friday his country was "not far" from war with Syria following cross-border attacks this week - words which highlighted the danger that the uprising against Syrian President Bashar al-Asaad will drag in its neighbours.

In a belligerent speech to a crowd in Istanbul, Erdogan warned the Assad government it would be making a fatal mistake if it picked a fight with Turkey.

The speech followed a Syrian mortar barrage on a town in southeast Turkey that killed five people on Tuesday.

Turkish artillery bombarded Syrian military targets on Wednesday and Thursday in response, killing several Syrian soldiers, and the Turkish parliament has authorised cross-border military action in the event of further aggression.

"We are not interested in war, but we're not far from it either," Erdogan said in his speech.

"Those who attempt to test Turkey's deterrence, its decisiveness, its capacity, I say here they are making a fatal mistake."

At the United Nations, the Security Council condemned the original Syrian attack and demanded that such violations of international law stop immediately.

The United States has said it stands by its NATO ally's right to defend itself against aggression spilling over from Syria's war.  

The cross-border violence was the most serious so far in the conflict, now in its 19th month, and underscored how it could flare across the region.

Turkey, once an Assad ally and now a leading voice in cals for him to quit, shelters more than 90,000 Syrian refugees in camps on its territory and has allowed rebel army leaders sanctuary.

Violence has also spilled over into Lebanon.