NATO will defend alliance member Turkey, which struck back after mortar rounds fired from Syria landed inside its border, the alliance's Secretary General Anders Fogh Rasmussen said at a meeting in Prague on Monday.

Turkey is becoming increasingly concerned about security along its border with Syria, in an area of the southeast where Ankara is also fighting an emboldened Kurdish insurgency.

"NATO as an organisation will do what it takes to protect and defend Turkey, our ally. We have more plans in place to make sure that we can protect and defend Turkey and hopefully that way also deter so that attacks on Turkey will not take place," Rasmussen said.

The NATO chief also welcomed a weekend agreement by Syrian opposition groups to put aside differences and form a new coalition. "A split opposition is of course a problem so we need a more inclusive and more united opposition," he said.

"What happened in Doha during the weekend was at least one big step forward. It remains to be seen whether this more united opposition is strong enough."

Turkey says it is talking to its NATO allies about the possible deployment of Patriot surface-to-air missiles to guard against a spillover of Syria's conflict. Rasmussen made no specific remarks on the possible deployment of Patriots.