Trump told reporters at a White House press gaggle that he was “in very deep discussions” about the case and would be able to report more “probably tomorrow.” The U.S. has issued a formal diplomatic message to Russia requesting additional information, according to reports. The Centers for Disease Control and Prevention said it is aware of and monitoring the case but noted there is no indication of a broader threat to the U.S.

The deceased worker, identified in Russian media as Darya Shipilova, was employed at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East. Russian health authorities have attributed her death to “pneumonia of an undetermined etiology,” though unconfirmed reports suggest she may have been exposed to the bacterium that causes pneumonic plague after breaking a test tube or returning from a field trip.

Kremlin spokesman Dmitry Peskov denied that a call between Trump and Putin had been scheduled and accused the media of spreading “false information.” He also said Russian officials were not aware of the U.S. diplomatic request for more information.

The World Health Organization has called for “timely, complete and transparent information sharing” under international health regulations. Director-General Tedros Adhanom Ghebreyesus said the WHO was in contact with Russian authorities and had requested further details on the case.

Differences remain in the accounts. Trump said the U.S. is “in very deep discussions” about the case, while Peskov denied any scheduled call. Russian officials have not confirmed the cause of the illness, while U.S. and WHO officials have expressed concern over a lack of transparency.

Trump also noted that the U.S. is prepared to offer help if the situation turns out to be more serious than claimed. “It’s a rough disease,” he said. “That’s a disease we used to be able to control, but somehow those microbes have gotten stronger and smarter. They’re like an army.”

The call with Putin comes as the Trump administration faces an October 18 deadline to decide which Russian entities to sanction under the recently enacted Lindsey O. Graham Sanctioning Russia and Iran Act. Ukraine has provided a list of targets it wants included in potential sanctions.