Hopes for a ceasefire taking hold in Syria this week dimmed today as Turkey renewed its shelling of advancing Kurdish militants and Washington demanded Moscow end air strikes on rebels.
Tensions over Syria have continued to mount despite the proposal from international powers in Munich on Friday for a "cessation of hostilities" within a week.
Defying US and French calls, Turkey today carried out a second day of shelling on a Kurdish-Arab alliance advancing in northern Aleppo province, prompting condemnation from Syria's government.
Turkey says it is targeting Kurdish forces it accuses of links to the banned Kurdistan Workers' Party (PKK) which has waged a decades-long insurgency against the Turkish state.
Washington has been working closely with Kurdish forces in northern Syria, and the Turkish attacks highlighted tensions within the US-led coalition battling the Islamic State group in Syria and Iraq.
Differences were also clear between Washington and Moscow, which backs international diplomatic efforts to resolve the Syria conflict but has also launched air strikes in support of President Bashar al-Assad, a key ally.
The White House said today that President Barack Obama had urged Moscow to end the strikes in a phone call with Russian counterpart Vladimir Putin.
Russia has long insisted that it targets only "terrorist" groups in Syria.
The Turkish shelling in northern Syria has added to an already complicated situation in Aleppo province, where regime forces have been making significant advances with backing from Russian air strikes.
The Syrian Democratic Forces (SDF), a US-backed Kurdish-Arab militia alliance, has also advanced in recent days, seizing the Minnigh air base and battling to take control of Tal Rifaat, a town held by mostly Islamist opposition fighters just 20 kilometres from the Turkish border.
Kurdish forces already control large parts of Syria along the border and Ankara is concerned the SDF will gain new ground.
Turkey's state-run Anatolia news agency said the shelling resumed for a second day today, with the Turkish army using howitzers on the border to hit Kurdish targets around the Syrian town of Azaz.
It said the shelling was in response to incoming fire and targeted the Kurdish Democratic Union Party, whose People's Protection Units (YPG) is a key component of the SDF.
The SDF announced the deaths of three fighters in the shelling, and the Britain-based Syrian Observatory for Human Rights saying a female civilian was also killed in the fire.
