ISTANBUL - Turkish Prime Minister Tayyip Erdogan said NATO is responsible for protecting his country's borders, newspapers reported on Thursday, after gunfire from Syria hit a refugee camp on the Turkish side, wounding four people."We have many options. A country has rights born out of international law against border violations," Erdogan was quoted as saying by Hurriyet daily and other newspapers. "Also, NATO has responsibilities to do with Turkey's borders, according to Article 5," added Erdogan, whose country is a NATO member.Article 5 of the NATO treaty declares that an armed attack against one of its members will be considered an attack against all members and allows for the use of armed force. It has been invoked only once, following the Sept. 11, 2001, attacks on the United States.Erdogan, speaking to reporters on board a plane returning from an official visit to China, also said fire had again crossed the border into Turkey from Syria on Tuesday.Erdogan said earlier this week that Turkey would take unspecified steps against Syria after stray bullets entered a refugee camp in the Turkish border province of Kilis on Monday. Two Syrians and two Turkish aid workers were wounded.He also accused Syrian President Bashar Assad of personal responsibility for killing civilians.Assad's forces have killed more than 9,000 people in the past year, according to a UN estimate. Damascus says rebels have killed more than 2,600 soldiers and security personnel.Turkey, once an ally of Assad, has been calling for an international effort to put an end to the fighting in Syria that began in an uprising in March 2011.