The United States has called for the release of two American citizens facing trial in North Korea on charges that Pyongyang says include "perpetrating hostile acts."
North Korea's official KCNA news agency said earlier that suspicions about Matthew Todd Miller and Jeffrey Edward Fowle had been confirmed by evidence and their own testimony.
"There's no greater priority for us than the welfare and safety of US citizens abroad," State Department spokeswoman Jen Psaki told reporters.
"Out of humanitarian concern for Mr Fowle and Mr Miller and their families, we request North Korea release them so they may return home," she added, without confirming reports that the men are facing trial, nor the charges levelled against them.
Swedish diplomats visited Fowle on June 20 and Miller on May 9 and June 21, she added.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The United States has no diplomatic relations with North Korea, and the Swedish Embassy acts as a go-between for Washington in dealings with Pyongyang.
Both men have agreed that the State Department disclose their names publicly.
Psaki renewed requests to free US missionary Kenneth Bae on humanitarian grounds.
Described by a North Korean court as a militant Christian evangelist, Bae is also being held in the country.
He was arrested in November 2012 and sentenced to 15 years' hard labour on charges of seeking to topple the government.
Miller, 24, was arrested in April after he apparently ripped up his visa at immigration and demanded asylum in the communist state.
Fowle, who entered the North on April 29, was arrested after the 56-year-old reportedly left a Bible at a hotel.
The State Department has issued a travel warning to North Korea that urges Americans to avoid travel to the reclusive state.
