Russia has presented no evidence to support the case against Gershkovich, which is proceeding in secret.
The Kremlin said Gershkovich had been carrying out espionage "under the cover" of journalism.
US Ambassador to the UN Thomas-Greenfield said on Wednesday she had spoken with her Russian counterpart Nebenzia to demand the immediate release of Wall Street Journal reporter Evan Gershkovich.
Gershkovich has been charged with espionage, in a move that human rights organizations are decrying and the Biden administration is fighting.
The Russian security services said in a statement it had opened a criminal case against Evan Gershkovich for suspected espionage.
For a town in Texas to be labeled incorporated, it must have at least 201 residents, the Post's report said.