Updated

Arab countries Oman and Iraq are involved in negotiations for the release of two Americans jailed in Iran for spying, officials said Thursday as efforts intensified over a $1 million bail-for-freedom plan.

A private plane from the Gulf state of Oman is in Tehran to carry away the pair if a deal is reached.

An Iraqi official, meanwhile, said a delegation of lawmakers also is in the Iranian capital to join the diplomatic talks on the release of Shane Bauer and Josh Fattal. They were detained along the Iran-Iraq border in July 2009 with their friend Sarah Shourd. She was released last September with mediation by Oman after a payment of $500,000 bail.

The high-level Iraqi and Omani intervention suggested movement on the complicated judicial and diplomatic dealings over the $500,000 bail deal for each American. Bauer and Fattal, both 29, were sentenced last month to three years each for illegal entry into Iran and five years each for spying for the United States. They have denied the charges and appealed the verdicts -- which leaves the opening for bail. Shourd's case remains open.

The Americans say they may have mistakenly crossed into Iran when they stepped off a dirt road while hiking near a waterfall in the semiautonomous Kurdish region of northern Iraq when they were detained.

A senior Iraqi government official told The Associated Press that Iraq's Shiite Prime Minister Nouri al-Maliki and President Jalal Talabani both support "efforts to help release American hikers on humanitarian grounds."

"Iraqis are acting as mediators with Iranian leaders," the official said on condition of anonymity due to the sensitivity of the issue.

An Omani official told the Associated Press that the plane belonging to the country's ruler is waiting to take the Americans out of Iran. At least two of Sultan Qaboos bin Said's close advisers are believed to be in Tehran, the Omani official said on condition of anonymity for fear of jeopardizing negotiations.

Neither official gave a timeframe of the Americans' release.

Oman has close ties with both Tehran and Washington and plays a strategic role in the region by sharing control with Iran of the Strait of Hormuz at the mouth of the Gulf, which is the route for 40 percent of the world's oil tanker traffic.

The Americans' defense attorney, Masoud Shafiei, said Wednesday he was moving ahead with the bail arrangements with Swiss Embassy officials, who represent U.S. interests in Iran because there are no diplomatic relations between the two countries. There were no details given on the source of the money.

However, Iran's powerful judiciary on Wednesday clouded the case by saying it was still reviewing the bail provisions. It was a potentially embarrassing rejection of President Mahmoud Ahmadinejad's prediction that their release could be in a matter of days.

The statement by the hard-line judiciary appeared to be a message that only its officials can set the timetables and conditions on any possible release and not the president, who is locked in a bitter power struggle with Iran's ruling clerics who control the courts.

It also could be a swipe at Ahmadinejad's hopes of timing the release the Shane Bauer and Josh Fattal with his expected arrival in New York next week for the U.N. General Assembly.

The rights group Amnesty International demanded the Americans' release without delay and urged Iran to put an end to "conflicting messages on the fate of the pair after more than two years in detention."

"The Iranian authorities must stop treating Shane Bauer and Josh Fattal as pawns, both in their dealings with the U.S. government and in domestic political rivalries," said Philip Luther, Amnesty International's Deputy Director for the Middle East and North Africa in a statement.

Washington has appealed for the two men to be released, adding that the U.S. is hopeful the freedom-for-bail deal will have "a positive outcome."