The United States criticized Russia on Wednesday for approving sales of fighter jets to Myanmar's military despite its deadly operations against Rohingya Muslims, warning that Moscow's actions could make the situation worse.

Russian defense officials used a visit to Myanmar this week to announce a deal to deliver six Su-30 fighter jets to the country's military. The Russian officials said Myanmar is also interested in buying Russian navy ships and land weapons.

State Department spokeswoman Heather Nauert called Russia's move to provide the jets "a good example of the challenges we face with certain governments." She said most of the world wants the Rohingya crisis resolved peacefully, and suggested Russia's actions would instead fuel more suffering and instability.

"This would seem to be an occasion where Russia could show solidarity through humanitarian assistance rather than potentially aggravating the situation through weapons sales," Nauert said.

The admonition comes amid heightened tensions between the U.S. and Russia, including over Moscow's military actions in Ukraine and elsewhere. On Tuesday, Secretary of State Rex Tillerson said Moscow was responsible for chemical weapons attacks in Syria for failing to rein in Syrian President Bashar Assad and his forces — an accusation that Russia firmly rejected.

The United States and many others refuse to sell weapons to Myanmar. In October, the U.S. restricted what limited non-weapons assistance it provides to Myanmar's military and its leaders, specifically cutting off those involved in the violence in northern Rakhine state — ground zero for the Rohingya crisis. Some 700,000 Rohingya have fled Myanmar to neighboring Bangladesh since August, when the military launched operations that the United States has described as "ethnic cleansing."

On Wednesday, former New Mexico Gov. Bill Richardson resigned from an international advisory panel on the crisis, calling it a "whitewash and a cheerleading operation" for Myanmar's civilian leader Aung San Suu Kyi. The sudden resignation cast a shadow over global efforts to deal with the crisis and raised further questions about Suu Kyi's leadership.

The six fighter jets aren't the first arms Myanmar has bought from Russia. In the past, the country has purchased MiG-29 fighter jets, Yak-130 combat trainers, Mi-17, Mi-24 and Mi-35 combat helicopters and other weapons, Alexander Fomin, a Russian deputy defense minister, said in Myanmar on Monday.

"I'm sure that Russia-Myanmar military-technical cooperation will develop further to allow Myanmar to build up a modern military armed with high-tech Russian weapons," Fomin said, according to the Russian news agency Interfax.

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Associated Press writers Vladimir Isachenkov and Jim Heintz in Moscow contributed to this report.

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Reach Josh Lederman on Twitter at http://twitter.com/joshledermanAP