The technician worked at the Irkutsk Research Anti-Plague Institute in Siberia. US officials said the administration contacted Russian authorities after the death and is seeking further details about the circumstances.
A US State Department spokesperson confirmed that additional information had been formally requested from the Russian government. Officials said Washington is also exchanging information with other countries as it assesses the situation.
US Secretary of State Marco Rubio said Russia should share more information with the international community, while warning that drawing conclusions or making assumptions would be irresponsible given the limited information available.
US officials said contact with Russian authorities has been ongoing since last Friday. President Donald Trump has also indicated that he may speak with Russian President Vladimir Putin about the matter.
One of the key questions for US officials is whether the technician died from pneumonic plague, a severe form of plague that can affect the lungs, or from another unidentified infectious disease.
The Irkutsk institute conducts research not only on plague but also on other dangerous diseases, including cholera, anthrax and brucellosis. US authorities are also seeking to determine whether any genetic modification may have been involved in the disease under investigation.
Russian authorities have quarantined the hospital where the technician was treated, while local media reports said around 200 people have been placed under medical observation.
The US has not imposed new travel restrictions on Russia so far and said it is monitoring the situation as more information becomes available. The National Security Council, State Department, Centers for Disease Control and Prevention and other federal agencies are reviewing the case.
The World Health Organization has also contacted Russian authorities in an effort to verify details of the incident.
Experts say pneumonic plague is a bacterial disease that can be fatal if untreated, but it can be effectively treated with antibiotics. They said the remote location of the research centre and the disease's limited ability to spread rapidly could help contain any immediate risk.
