WASHINGTON — An American tourist accused of espionage has been jailed in Russia for more than a year as his family members and lawmakers seek to step up pressure for his release.

The family of the American, Paul N. Whelan, says the Russian government is holding him in the hope of increasing his value in a potential trade for Russians imprisoned in the United States.

Relatives are now calling on Congress to penalize Moscow for its detention of Mr. Whelan, who was arrested last year while visiting Russia for a wedding. And lawmakers are pressing the Trump administration to escalate its efforts to secure his release.

Mr. Whelan’s arrest came shortly after a Russian citizen accused of trying to influence prominent Americans, Maria Butina, was imprisoned after pleading guilty to conspiring to act as a foreign agent. Some officials had hoped that Mr. Whelan would be freed once Ms. Butina had served her sentence. But she returned to Russia in October, and Mr. Whelan’s detention has been extended at least until March.