Turkey starts offensive to take Manbij from Kurds
Operation Euphrates Shield fighters turned towards Manbij, having successfully captured al-Bab from the Islamic State group last week.
Ankara has repeatedly lobbied the US over the continued presence of Kurdish fighters in Manbij that Turkish officials say are closely linked to the banned Kurdish organisation, the PKK.
"We stated earlier that Turkey will hit the YPG unless they withdraw from Manbij," said Turkish Foreign Minister Mevlut Cavusoglu on Thursday.
The Manbij Military Council, a local militia which receives support from the United States, quickly agreed a truce with Syrian rebel factions on Thursday, ceding control over a number of villages to the south-west of Manbij.
The Obama administration gave economic and military support to the Syrian Democratic Forces, an umbrella organisation of Kurdish-led militias in north Syria, a major source of frustration for Turkey.
Ankara has been locked in a four-decade war with PKK Kurdish separatists.
"We do not wish any of our allies to stand with terrorist groups," Cavusoglu said on Thursday.
A number of US military personnel are currently based in and around Manbij.
|The location of Manbij on a map of Syria
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The US position may yet change under the Trump administration. Turkey's Defence Minister Fikri Isik, signalled Washington had become more receptive to Turkish pressure.
"One of Turkey's must-do points is to definitely end the PKK-PYD presence in Manbij," said Isik.
The battle between Turkish and Kurdish fighters is the latest development in a complicated series of conflicts between various factions in the Syrian civil war, which began in 2011.The conflict began when President Assad's Baath regime responded to peaceful protests during the Arab Spring wave of uprisings with excessive military force.
This repression triggered an armed rebellion, fuelled by mass defections from the Syrian army.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions of people have been displaced both inside and outside of Syria.