Image caption Tehran allowed the mothers of the detainees to meet them last week

Two of the three US hikers detained in Iran for almost a year have become engaged to each other.

The pair - who are being held in a Tehran prison - plan to marry shortly after their release, their mothers say.

On Sunday, Iran's intelligence minister suggested a prisoner swap to secure the release of the three, who were arrested last July near the Iraq border.

Shane Bauer, Sarah Shourd and Josh Fattal have been accused of espionage.

The mothers of Shane Bauer, 27, and Sarah Shourd, 31, said they learnt the news during their reunion with their children on Thursday - the first since the trio allegedly strayed across Iran's border with northern Iraq.

The third detained hiker, Josh Fattal, 27, will be the best man at the planned ceremony, they said.

Shane Bauer proposed to Sarah Shourd while in the exercise area of Evin Prison in Tehran, and offered her a ring he made in his cell.

"Shane proposed to Sarah… he made a little ring out of the threads from his shirt and she has a ring," an emotional Nora Shourd, Sarah's mother, told the US network ABC.

"They are going to get married as soon as they have their freedom," she added.

"They have been in love for a long time. This was going on and they asked Cindy [Hickey, mother of Shane Bauer] and I if it was OK if they got married, and of course it is OK. We are happy to be families together," Mrs Shourd said.

Empty-handed

Tehran allowed the mothers of the three detainees to meet them last week, but ignored repeated pleas for their release.

The mothers had hoped to convince Iran to free their children during the visit, but after two days they flew home without them.

Tehran accuses the three of entering Iran illegally and having links to US intelligence.

Their families say they were hiking in northern Iraq's Kurdistan region and unintentionally crossed an unmarked border.

The three have spent 10 months in Iran's Evin prison. They have not been publicly charged.

US Secretary of State Hillary Clinton has called for the three to be freed.

The case has further strained relations between Washington and Tehran, which are at loggerheads over Iran's nuclear programme.