(NewsNation) —WNBA superstar Brittney Griner has been in a Russian jail for over four months now and calls on President Joe Biden to do something to bring her back to the U.S. are growing louder.

A billboard in Washington, D.C., is urging lawmakers, particularly Biden, to act with more urgency to free Griner. An online petition also urging Biden to take action has garnered more than 250,000 signatures.

Members of the U.S. Embassy in Moscow say they’re doing everything they can to free Griner.

“I can assure you that the United States government at the very highest levels is working very hard to bring Ms. Griner, as well as wrongfully detained U.S. citizens, safely home,” said Elizabeth Rood, the deputy chief of mission at the embassy.

Griner faces up to 10 years in prison after she was allegedly spotted at a Russian airport with cannabis vape cartridges. Griner’s trial began in Russian court on Friday.

Rumors of a possible prisoner swap involving Griner persist, particularly a deal centered around Griner and Russian arms dealer Viktor Bout, also known as “the merchant of death.”

Americans Alex Drueke, 39, and Andy Hyunh, 27, remain in Russian custody as well after they were captured fighting in Ukraine.

Now two British men are also in Russian custody, charged as mercenaries and possibly facing the death penalty. One of the men claims he was in Ukraine only to help others.