Syrian gunfire targeting refugees trying to cross into Turkey hit a camp on the Turkish side of the border on Thursday, the Anatolia news agency reported, the third such incident this week. 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 cross into Turkey. Syrian troops opened fire on about a dozen people as they tried to cross a zone planted with landmines on Thursday, Anatolia reported, although there were no reports of casualties. The gunfire caused panic in the Kilis border refugee camp in southeastern Turkey, although there was no report of casualties. It followed two similiar incidents this week, and came as a UN-backed ceasefire took effect in Syria and appeared to be largely holding. On Monday, shooting from the Syrian side killed two Syrians and hurt two Turks in the Kilis camp. Turkish media reported that fresh shots fired by Syrian forces hit the same camp on Wednesday, with no injuries. Angered by what he denounced as a “very clear violation of the border,” Prime Minister Recep Tayyip Erdogan signalled that Turkey may urge N to protect its border with Syria if the tension continues to escalate. “We have several options,” Erdogan was quoted as saying by the Sabah newspaper on Thursday. “First of all, there is an option of invoking Article 5 of the Nato treaty.” Article 5 stipulates that an attack against a Nato member is considered an attack against all members, but Nato action requires unanimous support from members of the North Atlantic Council, Nato’s decision-making body. Nato said it took its responsibility to defend its allies “extremely seriously.”