Turkish President Recep Tayyip Erdogan on Saturday slammed the United States over Washington's support for a Syrian-Kurdish militia that is fighting Islamic State.
The People's Protection Units (YPG) launched, together with more than 200 US special forces and Arab allies, an operation aimed at taking villages north of Islamic State's de-facto Syrian capital al-Raqqa and thereby increasing pressure on the extremist group.
"The support the US has given to the PYD and YPG ... I condemn it," he said in a speech made in Diyarbakir, a major city in the mostly-Kurdish south-east of Turkey.
Turkey has dubbed the YPG - the military wing of the Democratic Union Party (PYD) - a terrorist organization, citing its links to the banned Kurdistan Workers' Party (PKK) which has been locked in armed conflict with the state since 1984.
In his speech, Erdogan also referred to Kurdish militants as "atheists" and "Zoroastrians," adding that they do not share Turkey's values.
The US, while not entirely denying the links to the PKK, sees the groups as two separate entities. The YPG has proven to be the most reliable US ally on the ground in Syria fighting Islamic State, helping seize vast swaths of territory from the extremists.
This week, US special forces were photographed in Syria wearing uniforms with the YPG emblem, angering Turkey. The Pentagon has ordered the troops to remove the insignia but made no other moves.
Diyarbakir itself has seen heavy fighting in recent months between state forces and the PKK, after a ceasefire broke down last year amid mutual recriminations.
Many Kurds in Turkey's south-east complain of systemic discrimination. The PKK started as a separatist group but in recent years has focused on demanding greater rights and autonomy.
Islamic State is currently engaged in heavy fighting with Syrian rebel groups in northern Aleppo, some of whom are reportedly backed by Turkey, which is a generally a staunch supporter of the Syrian opposition to President Bashar al-Assad.
Several rockets have landed in Turkey in the past two days from areas seeing fighting. In the past Turkey, has blamed Islamic State for some rocket attacks. About 20 people have died from rockets on southern Turkey this year.
Turkey's state-run Anadolu news agency claimed the military killed 104 Islamic State fighters in response to the latest rockets, but there was no independent confirmation of this report from sources in Syria.