President Recep Tayyip Erdogan on Tuesday said that Turkey will expand its cross-border operations against Kurdish militants after 13 Turkish captives were killed in northern Iraq. On Sunday, Ankara said members of the outlawed Kurdistan Workers Party (PKK) killed the captives, who including police and military personnel, during a Turkish military operation against the group. Mr Erdogan repeated Turkey's complaint that it had not received enough expressions of international solidarity in its struggle with the PKK. "Whether you speak up or not, we know our duty. We will not give the terrorists a chance," Mr Erdogan told supporters from his AKP party in the Black Sea province of Trabzon. "We will expand our operations into areas where threats are still dense," he said. "We will stay in the areas we secure as long as necessary to prevent similar attacks again." The PKK, designated a terrorist group by Turkey, the United States and European Union, has waged a decades-long insurgency in Turkey's mainly Kurdish south-east. More than 40,000 people have been killed in the conflict. In the past two years, Turkey launched several cross-border operations to fight the PKK in northern Iraq, where the group has its stronghold in the Qandil mountains. On Monday, the US told Ankara that it blamed the PKK for killing the 13 Turks, after Turkey called an earlier US statement on the killings "a joke" and summoned the US ambassador. Turkish Defence Minister Hulusi Akar, briefing parliament on the operation after opposition parties criticised the government for failing to rescue the Turks, said the offensive was launched without ground support because of harsh conditions in the mountainous region.