MOSCOW—The U.S. and Russia struck a deal this month that promised to test the boundaries of trust between Washington and Moscow. Over a violent and tumultuous week in Syria, they couldn't overcome the distrust and animosity dividing them.

Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov hoped a successful cease-fire in Syria could pave the way toward joint military targeting against Islamist militants.

But just over a week ago, the U.S.-led coalition fighting Islamic State mistakenly bombed Syrian army positions, inflicting scores of casualties on government troops and prompting outrage in Moscow. Two days later, a deadly airstrike on an aid convoy delivering assistance to a rebel-held town escalated tensions, with U.S. officials blaming Russia for the attack.

The cease-fire all but collapsed, scuttling hopes the two sides would be able to cooperate in a meaningful away in fighting Islamic State and other militant groups.

By Saturday, Mr. Kerry and foreign ministers from the U.K., France, Italy, Germany and the European Union issued a denunciation of Russia's role in the escalating violence in Syria and said the bombing of the humanitarian convoy and the offensive in eastern Aleppo, among other actions, "blatantly contradicts Russia's claim that it supports a diplomatic resolution."

Messrs. Kerry and Lavrov haven't spoken since Friday and have no meetings planned, a State Department official said.

In Senate testimony on Thursday, Marine Corps Gen. Joe Dunford, chairman of the Joint Chiefs of Staff, made it clear the U.S. didn't trust Moscow. "I do not believe it would be a good idea to share intelligence with the Russians," he said.

Russian military insiders also scoffed at Mr. Kerry's proposal to ground all aircraft in northern Syria to allow shipments of humanitarian aid.

"They are saying, 'Let's have a no-fly zone, and that's our main weapon there,'" said Oleg Kulakov, a retired Russian colonel, referring to Russian air power. "Are you kidding? That means we give up to Daesh [Islamic State]."

The two countries had years of mutual suspicion to overcome. U.S.-Russia relations were at post-Cold War lows. Washington and its allies had slapped sanctions on Moscow after the Ukraine crisis and Russia's annexation of Crimea in 2014.

The U.S.-Russia relationship is complex. For instance, the U.S. believes the Kremlin played a constructive role in the move to increase international sanctions on Iran during President Barack Obama's first term and in pressuring Tehran to accept a final nuclear agreement last year. In Afghanistan, Washington and Moscow cooperated in moving supplies to support the U.S. and allied war efforts there.

At the same time, Russian President Vladimir Putin has regularly worked to counter U.S. interests and check American power, U.S. officials say.

Cold War-style rhetoric has heightened in recent weeks, with U.S. officials claiming Russian connections to the hacking of Democratic Party files. While Mr. Putin denies his country's involvement, the cyberattack has raised the specter of Russian interference in a U.S. presidential election.

Defense Secretary Ash Carter has been wary of coordinating and sharing intelligence with the Russians over Syria, echoing many senior officers' concerns, according to U.S. military officials.

Another apparent casualty is the amity between Messrs. Kerry and Lavrov, who engaged in months of diplomacy on Syria ahead of the cease-fire deal. In appearances at the United Nations last week, each blamed the other for the collapsing Syria peace efforts.

Mr. Lavrov said "foreign military interventions"â "code for U.S. actionsâ "were to blame for the chaos in the Mideast. Mr. Kerry said his Russian counterpart lived in a "parallel universe," referring to Russia's reflexive deployment of spin and denial following the bombing of the aid convoy.

Both sides would have needed to overcome serious distrust to set up joint operations against Islamist groups. Both sides worry the exchange of military information—as opposed to "deconflicting" operations to avoid accidents—presents serious intelligence risks.

Direct coordination of military operations with Russia would be "deeply counterproductive" to U.S. national-security interests, in part because of the risk the U.S. would reveal sensitive intelligence-collection capabilities, said Chris Harmer, senior naval analyst for the Institute for the Study of War in Washington.

Before the outright collapse of the cease-fire, Ruslan Pukhov, director of the Moscow-based think tank CAST, said he was optimistic the two sides could work together.

"If there is goodwill, we can always cooperate," he said. But, he added, "If there is no goodwill, we can always find a reason not to cooperate."

Jay Solomon, Felicia Schwartz and Gordon Lubold contributed to this article.

Write to Nathan Hodge at nathan.hodge@wsj.com

(END) Dow Jones Newswires

September 25, 2016 21:55 ET (01:55 GMT)

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