There are strong suggestions that the Washington Post's Iran correspondent Jason Rezaian, his wife, Yeganeh Salehi, and two American citizens were detained in Tehran this week, the paper reported Thursday.

It’s unclear who may have taken Rezaian, the Post’s correspondent in the country since 2012, but the paper said he and the others were possibly detained Tuesday in Tehran. The U.S. State Department said it was aware of reports of the detentions.

Douglas Jehl, the paper’s foreign editor, said the Post received “credible reports” that the four were detained. A spokesman for the Iranian Mission at the United Nations told the paper that Iranian diplomats were looking into the reports.

Rezaian, 38, is one of three U.S. citizens being held (he has dual U.S.-Iranian citizenship); the others are freelance photojournalists whose names have not been released. Salehi is an Iranian citizen who has applied for permanent residency in the U.S.

“Our highest priority is the safety and welfare of U.S. citizens abroad,” State Department spokeswoman Marie Harf told the Post. She didn’t comment further.

Jehl said in a statement that Rezaian “is an experienced, knowledgeable reporter who deserves protection and who merits respect.

“We are deeply troubled by this news and are concerned for the welfare of Jason, Yeganeh and two others said to have been detained with them,” Jehl added.

Salehi is a correspondent for the National, a newspaper based in the United Arab Emirates.