U.S. President Barack Obama speaks during a news conference at the close of the Association of Southeast Asian Nations (ASEAN) summit at Sunnylands in Rancho Mirage.

President Barack Obama in a telephone call with Turkey’s President Recep Tayyip Erdogan Friday urged the Ankara government and Kurdish YPG forces to “show reciprocal restraint” in northern Syria.

“President Obama stressed that YPG forces should not seek to exploit circumstances in this area to seize additional territory, and urged Turkey to show reciprocal restraint by ceasing artillery strikes in the area,” a White House statement said.

In response, in a phone conversation that lasted one hour and 20 minutes, Ankara said Obama had told his counterpart President Tayyip Erdogan that Turkey had a right to self-defense, and expressed worries over advances by Syrian Kurdish militias near Turkey’s border.

Earlier on Friday, Erdogan had said U.S.-supplied weapons had been used against civilians by a Syrian Kurdish militia group that Ankara blames for the deadly suicide bombing this week.

The State Department, which sees the Syrian Kurdish YPG fighters as useful allies against ISIS, said the United States had “not provided any weapons of any kind” to the group.

The issue risks driving a wedge between the NATO allies at a critical point in Syria’s civil war, as the United States pursues intensive talks with Syria’s ally Russia to bring about a “cessation of hostilities.”

Turkey has blamed the YPG for the suicide car bomb attack on Wednesday that killed 28 people, most of them soldiers. But a Turkey-based Kurdish splinter group has claimed responsibility for the bombing and threatened more attacks.

Obama expressed his condolences to Erdogan over the bombing in the Turkish capital, the White House said.

Before the call with Obama, Erdogan said he was saddened by the West’s refusal to call the Syrian Kurdish militia terrorists, and would explain to the U.S. president how weapons provided by the United States had aided them.

“I will tell him, ‘Look at how and where those weapons you provided were fired’,” Erdogan told reporters in Istanbul.

However, Syria’s government has accused Turkey of artillery shelling inside Syria and said it is an “outrageous violation” of international law.

In a statement published by the state-run SANA news agency Saturday, it accused Turkey of committing “crimes” against the Syrians by firing artillery shells at areas in the northern province of Aleppo.

It added that a number of civilians were injured by the artillery fire that targeted Tel Rifaat, Malikiyeh and other towns.

Turkey has in the past week kept up a cross-border artillery shelling campaign against U.S.-backed Syrian Kurdish militia positions in Syria. It has also threatened ground action, saying it was exercising its right to self-defense and responding to fire from Syrian soil.

The main Kurdish group in Syria has denied firing at Turkey from Syria.

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