US-backed forces were supposed to assault ISIS capital two weeks ago

The start date of the offensive to oust Islamic State fighters from the city of Raqqa and end the terror group's state-building project has been announced several times in the past few months, often with great fanfare by commanders in the Kurdish-led Syrian Democratic Forces, the United States' ground ally in northern Syria.

The last announcement came in March when Kurdish commanders said an assault on the city would begin April 1.

Two weeks later that start date, like many others, has come and gone, prompting the months-long question: when will the U.S.-backed SDF offensive shift gears from isolating Raqqa, which is hemmed in on three sides now, to mounting an assault to retake the capital of the jihadists' self-styled caliphate?

Over the weekend, Syrian President Bashar al-Assad told the French news agency AFP he would support whomever wants to oust Islamic State militants from Raqqa, but mocked the delay in an assault on the city, which U.S. officials believe is being defended by around 4,000 IS fighters.

"What we hear is only allegations about liberating Raqqa. We've been hearing that for nearly a year now, or less than a year, but nothing happened on the ground," he said. "It's not clear who is going to liberate Raqqa...It's not clear yet."

No firm answer about a new start date was forthcoming on April 15 from U.S. Secretary of Defense Jim Mattis when he met in Washington with his Turkish counterpart, Fikri Isik.

The Turkish defense minister again complicated the U.S. effort to choreograph an agreement among multiple local and international players about a Raqqa offensive by pressing Ankara's long-standing demand for the U.S. to end its alliance with the Kurdish People's Protection Units, or YPG, whose fighters dominate the ranks of the SDF.

There were no signs that the Turkish request made persistently by Ankara in recent months, and relayed by President Recep Tayyip Erdogan during a February phone call with U.S. President Donald Trump, will be heeded.

U.S. officials say they envisage the Raqqa battle will resemble the fight in neighboring Iraq, where local indigenous forces have been waging the struggle to retake the northern city of Mosul, the last IS major urban stronghold in that country.

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Some 500 U.S. special forces soldiers deployed in northern Syria are helping to train and advise SDF units.

Mattis later said at a press conference the U.S. remains in solidarity with Ankara when it comes to fighting Islamic State militants and Turkey's outlawed Kurdistan Workers' Party, or PKK, but he made no mention of discontinuing the alliance with the YPG, the armed wing of Syria's Democratic Union Party, or PYD.

The Turks, who fear the emergence of a Kurdish state in north Syria, maintain there's no real distinction between the PYD and the PKK, which has been waging an insurgency in Turkey for more than three decades.

Mattis cited the long security relationship between the U.S. and Turkey, dating back to 1952 when Turkey joined NATO; but, in the wake of the April 16 constitutional referendum that greatly enhances the Turkish president's powers, analysts say it is unclear how much Erdogan values his country's alliance with the West, and whether his slim victory will embolden him to disrupt a Raqqa assault by the SDF.

Earlier in April, Erdogan ramped up the pressure on Washington, saying his government is planning new offensives in northern Syria this spring against groups deemed terrorist organizations by Ankara, including IS and the PYD's militia.

In March, Turkish forces escalated attacks on the YPG in northern Syria, forcing the U.S. to deploy a small number of forces in and around the town of Manbij to the northwest of Raqqa to "deter" Turkish-SDF clashes and ensure the focus remains on Islamic State.

Meanwhile, Raqqa is being pummeled by airstrikes mounted by U.S.-led coalition forces and Syrian warplanes.

Local anti-IS activists say the air raids fail to distinguish between military and non-military targets; however, with IS fighters seeded throughout the city and surrounding villages, being able to draw a distinction is become increasingly challenging, say U.S. officials.

"Civilians are now [caught] between the criminal terrorists on one side and the international coalition's indiscriminate bombing on the other side," said Hamoud Almousa, a founding member of the activist network Raqqa is Being Slaughtered Silently, which is opposed to an assault on the city being led by the YPG.

"Liberating [Raqqa] does not come by burning it and destroying it over its people who have suffered a lot from the terrorist group's violations," he added.

The Syrian Observatory for Human Rights, a London-based monitoring group that relies on a network of activists for its information, said that four civilians — two women and two children — were killed April 17 in an airstrike believed to have been carried out by coalition warplanes on the Teshreen Farmarea north of Raqqa.

The Observatory says between March 1 and April 10, airstrikes killed 224 civilians. They included 38 children under the age of 18, and 37 women.

Another mainly Arab anti-IS activist network, Eye on the Homeland, complains at the lack of international condemnation about the civilian casualties from the airstrikes, arguing civilians caught in the conflict are being treated inhumanely.

"We assert that the liberation of civilians from all forms of terrorism requires that military forces acting in the area avoid civilian killing, displacement, and the destruction of their properties whenever possible," the network said recently on its website.

It warned the deaths will "be used to by terrorist organizations in their propaganda to convince civilians that these military forces do not have their interests at heart" and will "only further fuel radicalization."