The U.S. and Russia have been trading barbs since President Donald Trump ordered airstrikes on the Assad regime’s military assets in Syria last week, but now Russian President Vladimir Putin has closed the door on a face-to-face meeting with Secretary of State Rex Tillerson when the U.S. top diplomat visits the country later this week.

Russia has long supported Syrian President Bashar Assad and refutes the U.S. claim that the dictator ordered the recent chemical weapons attack in Syria that killed innocent people, including many children.

“We have not announced any such meetings and right now there is no meeting with Tillerson in the president’s diary,” spokesman Dmitry Peskov told reporters on a Monday press conference call, according to Reuters.

Before Tillerson became Secretary of State, he was the CEO of ExxonMobil, a job that included dealings with the Kremlin. In 2013, Putin presented Tillerson with the Russian Order of Friendship award.

Tillerson is expected to meet with his Russian counterpart, Foreign Minister Sergei Lavrov, during his stop in Moscow, according to Reuters.

Reuters reported that Putin regularly met with John Kerry, Secretary of State under Barack Obama.

“Reacting to media reports that Tillerson would use his visit to press Moscow to stop supporting Syrian President Bashar al-Assad, Russia’s closet Middle East ally, Peskov called that a non-starter,” Reuters reported.

“Returning to pseudo-attempts to resolve the crisis by repeating mantras that Assad must step down cannot help sort things out,” Peskov said.

Other thorny issues may surface during Tillerson’s visit to Moscow, including Russia’s alleged interference in the 2016 U.S. presidential election, its violation of an arms control treaty, and finding common ground on fighting radical Islamic terrorism in Syria.

Tillerson had some tough words for Russia on Thursday about the chemical weapons attack.

Speaking from Trump’s Mar-a-Lago estate in Florida, where Trump was meeting with Chinese President Xi Jinping, Tillerson cited Russia’s 2013 agreement to oversee the destruction of Syria’s chemical stockpile, saying Russia has “clearly failed in its responsibility” to eliminate those weapons.

“Either Russia has been complicit or Russia has been simply incompetent on its ability to deliver,” Tillerson said.

U.S. military officials have said they are certain Assad is responsible for the attack.

“We highly suspect, and in fact, there’s no credible alternative to a Syrian regime air attack as the source of the chemicals that killed so many Syrian civilians,” a military official said.

“ISIS has experimented with mustard agents, blister agents, not nerve agents,” an official said. “But this is well beyond the technical capability of the opposition.”