WASHINGTON (AFP) - US Secretary of State Hillary Clinton said Thursday she hoped that Iran would free three imprisoned American hikers soon on humanitarian grounds, following an "emotional" meeting with their families.

Supporters of the hikers who wandered over the the Iraqi border into Iran in the summer announced that vigils would be held across the United States and around the world on Sunday to mark their 100th day of detention.

"I would hope that the government of Iran would free them on (a) humanitarian and compassionate basis as soon as possible and return them home to their families," Clinton told reporters.

The chief US diplomat added that the US government was "exploring every angle" for the release of Shane Bauer, Sarah Shourd and Josh Fattal, adding she briefed their families about the efforts.

"It was an emotional meeting, and I described to the families everything that we are doing," she said. "I was impressed by their strength."

The three were detained in July after crossing into Iran while hiking in Iraqi Kurdistan.

A diplomat from Switzerland, which represents US interests in Iran, visited the three Americans in Tehran's notorious Evin prison last week, according to their families, who said the trio were "in good physical shape."

In a statement on Thursday, relatives, friends and supporters said they will hold "Vigils of Hope" across the United States and around the world on Sunday, "in the latest effort to press for the hikers' release."

They said the vigils will be held at "more than 20 locations from southern California to northern Vermont and in Canada, China, Colombia, India, Mexico, South Africa, Sweden, the United Kingdom and Vietnam."