Washington's top diplomat for the Near East, Anne Patterson, had a number of meetings in Oman with parties involved in the Yemen conflict, "including with representatives of the Huthi," said State Department spokeswoman Marie Harf.
Patterson, who also traveled to Saudi Arabia for talks on the conflict, wanted to persuade actors in the conflict to take part in a proposed peace conference in Geneva, she said.
A conference on Yemen was scrapped four days before it was due to be held on May 28, dealing a blow to UN efforts to broker peace in a country where at least 2,000 people have been killed since March.
Pictures released by Oman's official ONA news agency showed journalist Casey Coombs being stretchered into an ambulance with a brace around his head.
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Released along with him was a Singaporean, according to Omani state media, which said they were on their way home.
Coombs, who had been working freelance in Yemen since 2012, writing for publications including Time magazine and The Intercept, had been held by the Huthis for two weeks, the Committee to Protect Journalists said.
In an article he wrote for The Intercept last month, Coombs said he had been trying to leave the country, but was struggling to find a safe route out.
The United States said at the weekend it was working to secure the release of "several US citizens" held in Yemen.
Washington has provided intelligence and logistical support for the air campaign but has called for a political solution to the conflict.
The UN's World Food Programme warned today that "child malnutrition rates in Yemen are among the highest in the world".