The United States is closely tracking the suspected pneumonic plague death of a researcher at a remote anti-plague laboratory in eastern Russia, Secretary of State Marco Rubio said Tuesday, urging Moscow to provide more information about the case. Speaking at a press conference in Reykjavik, Iceland, Rubio said multiple U.S. agencies were monitoring developments “hour-by-hour.” He cautioned against drawing conclusions before more facts are available, saying the United States could not respond proactively without greater transparency from Russia. “It would be irresponsible for me here to sit and speculate because we just don’t have all the information yet,” Rubio said. He added that Russia should share more information with the international community so countries can better prepare a response. Russian officials say they have placed more than 200 people under observation. They also reported that tests on a sample taken after the researcher’s death found no pathogens connected to her work. The cause of death remains suspected, rather than confirmed, as pneumonic plague. The death has raised concern in Europe. Rubio’s call for information comes as public health agencies seek details about what happened and whether anyone else may have been exposed.