The attorney, Masoud Shafiei, said he could not complete the paperwork on the $1 million bail deal because a second judge who must sign the documents is on vacation until Tuesday. One judge already signed the papers Saturday.
"I have no choice but to wait until Tuesday," Shafiei told The Associated Press.
Shane Bauer and Elkins Park native Josh Fattal, both 29 years old, have been jailed for more than two years in a case that has deepened the mistrust between Iran and the United States.
They were detained along the Iran-Iraq border in July 2009 with their friend Sarah Shourd. She was released last September with mediation by the Gulf nation of Oman after $500,000 was paid.
The men were convicted of spying for the United States and illegally entering Iran and were each sentenced last month to eight years in prison. They denied the charges and appealed the verdicts, opening the way for the possible deal to free them in exchange for $500,000 bail each.
They say they were just hiking in Iraq's scenic north and may have mistakenly crossed an unmarked border with Iran.
Iran's Foreign Minister Ali Akbar Salehi said Saturday the courts are willing to commute the Americans' sentences in the "near future" as a gesture of Islamic mercy, but did not say when the pair could be released.
However, Mohammed Javad Larijani, the head of Iran's Human Rights Council and a brother of the country's head of the powerful judiciary, said the men's "crime was not limited to illegal trespassing." Bauer and Fattal were spying for the U.S. and "we do not award the spies," Larijani told the semiofficial Fars news agency Sunday.
The mixed signals could reflect the bitter internal political feuds inside Iran between President Mahmoud Ahmadinejad and the country's ruling clerics, who control the courts. Ahmadinejad and his allies are accused of trying to challenge the power of Iran's Islamic establishment.
The first word of the bail plan for Bauer and Fattal came earlier this week from Ahmadinejad, who said the Americans could be freed in a matter of days. But Iran's hardline judiciary then responded that the bail provisions were still under review.
Mediators from Iraq and Oman have asked Iran to free the Americans on humanitarian grounds.
The Gulf state dispatched a plane to Tehran on Wednesday to carry the pair out of Iran when a bail-for-freedom deal is reached. Swiss officials also are involved as representatives of U.S. interests in Iran, which has no diplomatic ties with America.
Officials in Oman were tightlipped about their mediation efforts for fear of jeopardizing the deal. At least two close advisers of the Omani ruler were in Iran. Also, Oman's foreign minister, Yousef bin Alawi, discussed "issues of mutual interest" with Iran's top diplomat twice this week, Iran official news agency IRNA reported.
Oman has close ties with both Tehran and the Washington and plays a strategic role in the region by sharing control with Iran of the Strait of Hormuz at the mouth of the Persian Gulf - the route for 40 percent of the world's oil tanker traffic.
U.S. Secretary of State Hillary Rodham Clinton said Thursday the United States continues to hope the Americans will be released, adding that Washington has received word through a number of sources that the two will be returned to their families.
The last direct contact family members had with Bauer and Fattal was in May 2010 when their mothers were permitted a short visit in Tehran.
Since her release last year, Shourd has lived in Oakland, California. Bauer, a freelance journalist, grew up in Onamia, Minnesota and Fattal, an environmental activist, is from suburban Philadelphia.
Bauer proposed marriage to Shroud while in prison.
Surk reported from Muscat, Oman.