Brittney Griner may have been the most well-known American whose overseas detention was deemed unlawful by the United States. State Department, but she wasn’t the only one: According to research, the number of Americans who have been wrongfully or unjustly detained by foreign governments has sharply increased in recent years.

How many Americans are being held wrongful by state actors has not been officially counted by the State Department. However, researchers for the James W. Foley Legacy Foundation, which represents wrongful detainees, hostages, and their families, have discovered a rise in the number of Americans being held by foreign governments.

According to an interview with Cynthia T. Loertscher, the director of research, hostage advocacy, and government affairs for the Foley Foundation, “over the last 10 years we’ve seen a 175 percent increase in incidents of Americans being wrongfully detained.”

An email requesting comment from a State Department spokesman did not receive a prompt response. A senior State Department official claimed in July that 40 to 50 Americans were being imprisoned illegally by other countries.

The foundation, which bears the name of the journalist James Foley who was killed in Syria in 2014 by the Islamic State, released a report in September that revealed an increase in wrongful detentions.

The report found that between 2012 and 2022, there were an average of 34 Americans held illegally by foreign governments annually, a 580 percent increase from the prior decade’s average of five Americans held annually.

In 2022, “at least 19 countries had either wrongfully detained or continued to hold a U.S. national in captivity,” the report found, compared to only four countries at the turn of the century.

Three-quarters of American citizens who are currently being held unlawfully are being held in detention, according to the report, in Iran, China, Venezuela, Syria, and Russia.

As he discussed Ms. Griner’s release on Thursday morning, President Biden brought up the subject.

He said at the White House, “I don’t want any American to sit wrongfully detained one extra day if we can bring that person home.” “Up to this point, my administration has returned home dozens of Americans who had been wrongfully imprisoned or held captive abroad, many of whom had been held since before I took office. And on this day, we also think of the other Americans who are wrongfully held captive or detained anywhere in the world, including Russia. It is still a top priority for my administration and each employee involved in this to reunite these Americans with their families.

The Foley Foundation’s founder and president, Diane Foley, praised the efforts made by the Biden administration to release Ms. Griner. It was “heartbreaking that Paul Whelan is not also on that flight home with Brittney,” she said in a statement, urging the administration to keep up the pressure on Russia to free Paul Whelan, an American serving a 16-year sentence there on espionage charges that the U.S. government has said were false.

“We haven’t forgotten about Paul Whelan, who has been wrongfully detained in Russia for years,” Vice President Biden said at the White House.

“Sadly, for totally illegitimate reasons, Russia is treating Paul’s case differently than Brittney’s,” he said. “And while we have not yet succeeded in securing Paul’s release, we are not giving up. We will never give up.”