Turkey will undoubtedly invoke NATO's mutual defence treaty if subjected to a serious attack from neighbouring Syria, a senior Turkish official said on Wednesday.

"This is one of the options," said the official who wished to remain anonymous.

"Right now there is no such situation requiring Turkey to invoke Article 5, but we will consider this option in the event of a serious attack on our sovereignty."

He was referring to the clause which stipulates that an attack against a member of the North Atlantic Treaty Organisation is considered an attack against all members of the alliance.

Syrian gunfire targeting refugees trying to cross into Turkey hit a camp on the Turkish side of the border last month, leaving two Syrians dead, according to eyewitnesses.

After the incident, Ankara has said it might call in NATO to help protect its border, amid heightened tensions with Damascus over the deadly conflict in Syria, which has seen thousands of people crossing into Turkey.

When asked on April 12 what Turkey's response would be to conflict spilling over the Syrian-Turkish border, Prime Minister Recep Tayyip Erdogan said that "we have several options."

"First of all, there is an option of invoking Article 5 of the NATO treaty," he said.

The Turkish official said there had been no serious attack thus far emanating from Syria against Turkey but "if it happens, we have the right to invoke Article 5 like each member state of the alliance. This is our natural right."

NATO invoked Article 5 of the Washington Treaty for the first time in its history following the 9/11 attacks against the United States.

The Syrian crisis is expected to appear on the agenda of NATO summit in Chicago on May 20-21, the official added.