ISTANBUL, Turkey — As evidence mounts that Russia is deliberately targeting civilians in Syria with cluster bombs and other anti-personnel weapons, what has long been a nagging question about Washington’s policy has now taken on real urgency: Why is there no comment from the U.S. government is to confirm or refute the allegations of war crimes?

A Human Rights Watch report out Thursday documents how Russian aircraft dropped cluster bombs on an informal fuel market outside Termanin, a village in Idlib province, on July 11, killing 10 and wounding more than 30 people. The victims were all civilians and included two who were first responders.

According to HRW, three fighter aircraft, two of them SU-34s flown only by Russia, and an SU-24 that’s in both the Russian and Syrian air force, launched eight attacks: the first two of them using cluster bombs—large canisters containing dozens of tiny bomblets that scatter through the air and across the ground. Many do not explode—at first, but may kill and maim days, months, even years later.

HRW noted that cluster bombs are “inherently indiscriminate, and repeated strikes on the target even after first responders arrived make the attack unlawful.”

Russia is not a party to the international accord banning cluster munitions, but it is party to the 1949 Geneva Conventions, which list indiscriminate attacks as a grave breach. So are the U.S. and Syria. The conventions not only require their signers to uphold the stated rules, but to see to it that they are upheld by others.

The report provides meticulous backup for witness accounts on the role played by the SU-34s. There are videos shot at the time of the attack, and Russian websites say Russian aircraft carried out the attacks.

The evidence raises questions. Was the U.S. government, which has extensive airborne surveillance capacity in the region, aware of the Russian role in the bombings, and if so why hasn’t it said anything?

One full day before HRW issued its latest report, The Daily Beast asked the State Department what it knows about Russia’s role:

Were Russian aircraft bombing in the area that day? Have they dropped cluster munitions on civilians there or in other locations? Has the U.S. representative raised this incident at the U.S.-Russian forum monitoring a declared cease-fire, and if so, what was the response? How many other such incidents has the U.S. raised with the Russians?

Twenty-four hours later, there was no answer.

Anticipating a non-response, The Daily Beast asked the State Department how the U.S. expects to bring Russia into compliance with the conventions’ ban on indiscriminate attacks if it doesn’t publish or otherwise inform the public of its intelligence findings.

There was no response.

One reason for U.S. silence about Russian violations is that the Obama administration has classified its intelligence findings in order to “protect sources and methods” of collection. Making that information public “would also set a precedent of the U.S. reporting on foreign military activity,” a senior administration official told us earlier this year. “Where do you draw the line?”

But that leaves open the question of whether the U.S. government has raised the issue with Russia and how Russia responded. It also raises the larger question of whether international law as drafted after World War II will be respected when a major power violates the laws of armed conflict with impunity and there’s no public protest from the United States.

Ever since Russia began its bombing campaign Sept. 30, the U.S. response has been largely “hands-off.”

Despite public pleas by Syria’s moderate opposition and private urging by neighboring states like Turkey, the U.S. has not stepped up aid to moderate rebel forces already receiving U.S. military support, nor has it threatened the use of force or any other measures that would raise the price for Russian intervention.

Instead, the administration has sought a cease-fire through what it calls diplomatic means, which it hopes will lead to a negotiated settlement of the Syrian conflict.

Secretary of State John Kerry has been negotiating nonstop with Russian officials in hopes that together they might bring an end to hostilities and the resumption of negotiations as early as Aug. 1.

But the Russian and Syrian governments in the past month instead have gone for the kill in Aleppo, Syria’s biggest city, and now the timetable for negotiations appears to be put off until the end of August.

Syrian forces, augmented by Iranian ground troops and the Lebanese Hezbollah milita and Russian air power, cut the last road to the rebel held enclave July 10. Besides surrounding the eastern part of Aleppo, which has a population of at least 300,000, the regime-led forces destroyed four of the eight hospitals and the only blood bank and forensic lab. They also dropped barrel bombs and other munitions on residential areas.

But the Obama administration has yet to draw attention to the biggest siege since Serb forces surrounded Sarajevo from 1992 to 1995.

Throughout the Russian intervention in Syria, the administration has refused to clarify whether Russia or Syria is responsible for the destruction of hospitals, schools, mosques, and infrastructure protected by international law.

In early May, after airstrikes destroyed a camp for displaced persons in northern Idlib province, Russia rejected charges that its aircraft were responsible. After Russia and the Syrian regime were accused of bombing several major hospitals in rebel-held Aleppo, a hospital in regime-held Aleppo came under attack also in early May. The government blamed rebel forces, but those forces said they didn’t have weapons that could have reached the target and said the government had launched the attack in order to claim that the rebels were a criminal force.

The State Department continually ducked all questions on who was really responsible for any of these attacks.

Given that the U.S. intelligence gathering capabilities in the region are extensive, especially where warplanes are concerned, Washington almost certainly knows who is doing what from the air. But there are none so blind as those who will not see, and the official refusal to acknowledge culpability undermines the efforts of those organizations and journalists who are trying to get at the truth.

Early in June, after repeated requests for clarification, a State Department official sent a formal response. “On background, I looked into this with our Syria team, and the assessment into these incidents have not been definitely concluded,” he said.

That was it. No clue was given as to what that assessment might be.

Increasingly, it appears that the administration has written off Aleppo and with it the popular rebellion against Syrian strongman Bashar al-Assad. Whatever criticism the U.S. may have stated when Russia began its armed intervention, officials now rationalized it as Moscow’s rescue of a longtime ally.

In March, a senior U.S. official said that Russia had intervened because rebel forces were advancing so fast that they threatened the survival of the Assad regime. There was great concern in Russia “about potential catastrophic success” under which “Assad collapses, but so do all the Syrian state institutions.”

The Russian intervention has returned Syria “to the stalemate,” the official said.

On Wednesday, the State Department cast the Russian intervention in the context of Moscow’s long-term alliance with Damascus.

Russia has “a historic defense relationship with Syria that goes well back before the current conflict,” department spokesman John Kirby told reporters. “They’ve had basing there. They’ve had troops there. They’ve had a presence there. So it came as a shock to no one in the State Department that as the civil war progressed in Syria, that they would have interest in how things were going,” he said.

The question of the moment, however, is why Washington seems to have no interest in the war crimes Russia commits as part of that “interest in how things were going.”