Russian Foreign Minister Sergey Lavrov said Friday that the Kremlin was “ready to discuss” a possible prisoner exchange involving American basketball star Brittney Griner but strongly warned the U.S. against publicizing the negotiations.

“We are ready to discuss this subject, but only within the framework of the (communication) channel established by presidents Putin and Biden,” Lavrov told a press conference on a visit to Cambodia.

“There is a special channel established by the presidents and despite certain public declarations, it is still functional,” he added.

“If the Americans again try to engage in public diplomacy and make loud statements about their intention to take certain steps, it’s their business, I would even say their problem,” Lavrov said. “The Americans often have trouble observing agreements on calm and professional work.”

In Moscow, Kremlin spokesman Dmitry Peskov echoed Lavrov’s statement but more sternly.

“The U.S. already has made mistakes, trying to solve such problems via ‘microphone diplomacy.’ They are not solved that way,” said Peskov.

He emphasized that discussions on a possible trade should be held through the confidential channels that Putin and Biden have established.

“Such mechanisms exist, but they will be thrown into doubt if the discussion continues in the public domain,” Peskov said, adding, “If we discuss any nuances related to the issue of exchange via media, no exchange will ever take place.”

The U.S. has reportedly made a “substantial proposal” to Russia to release Griner and Paul Whelan, another American detained in Russia on espionage charges.

The deal would allegedly involve swapping Griner and Whelan for Viktor Bout, a notorious Russian arms trader labeled as the “Merchant of Death.” He is serving a 25-year sentence in the U.S. after being convicted of conspiracy to kill U.S. citizens and providing aid to a terrorist organization in 2012.

However, there has been no official announcement from Washington that Bout has been offered in a prisoner swap.

Bout’s wife, Alla, expressed her sympathies to Griner’s family on Friday, saying she hoped her husband and the U.S. athlete would be able to return home.

“Sympathy has no citizenship and nationality, it is a universal human emotion,” she told Russian news agency RIA Novosti, adding that she hopes Russia and the U.S. would “come to an agreement.”

Griner, a two-time U.S. Olympic champion and eight-time all-star with the WNBA’s Phoenix Mercury, has been detained in Russia since February 17 upon her return to play for a team in Russia, where she has competed since 2014.

Police at Moscow’s airport reportedly found vape cartridges containing cannabis oil in her luggage.

A judge convicted the 31-year-old athlete Thursday of drug possession and smuggling and sentenced her to nine years in prison.

Blinken said Griner’s conviction and sentence “compounds the injustice that has been done to her.”

“It puts a spotlight on our very significant concern with Russia’s legal system and the Russian government’s use of wrongful detentions to advance its own agenda using individuals as political pawns,” he said.