A telephone call between the presidents of the United States and Turkey produced conflicting accounts of the conversation about Turkey’s military foray into Syria in pursuit of Kurdish rebels, underscoring the deep fissures dividing the NATO partners.

Turkey opened a new front in the seven-year war in Syria last week, using jets, ground forces and proxy fighters from the Free Syrian Army to pound the US-backed People’s Protection Units (YPG) in the northwestern province of Afrin, a relatively stable area held by Syrian Kurds.

Now, Turkish President Recep Tayyip Erdogan says his armed forces will push to the strategic town of Manbij, which is controlled by the Kurds and where some of the estimated 2,000 US special forces in Syria are deployed as part of the US-led coalition fighting the Islamic State (IS). Unconfirmed reports emerged on Thursday that Turkish warplanes hit Kurdish weapons stores in Manbij.

In a phone call late Wednesday, US President Donald Trump warned Erdogan “to avoid any actions that might risk conflict between Turkish and American forces” and that “escalating violence in Afrin, Syria, risks undercutting our shared goals in Syria,” according to the strongly worded statement from the White House.