About 400 Iranian exiles have been transferred from their long-held camp in north-western Iraq.
They are members of the People's Mujahideen Organisation of Iran (PMOI), based at Camp Ashraf since the 1980s.
It is the first step of a process that aims to see the entire 3,400-strong community expelled from Iraq.
But members of this advance party are complaining bitterly that their treatment has fallen far short of that promised by the UN and US.
The exiles, who are opposed to Iran's Shia clerical rulers, were welcomed by former Iraqi leader Saddam Hussein but have fallen out of favour with Iraq's new Shia-dominated leadership.
Relations with the Iraqi government deteriorated still further last April, when an Iraqi army raid on the camp left 34 residents dead, according to the UN.
At first, they refused to countenance leaving Camp Ashraf, but the UN has been trying to broker a compromise. In December the group's Paris-based head Maryam Rajavi agreed that a first contingent of 400 would move in what she called a "goodwill gesture".
The Iraqi government has extended a deadline for the camp to be shut down to the end of April.
On Saturday, the first group arrived at Camp Liberty near Baghdad, but complained that they had been searched for almost an entire day before they were allowed to leave Ashraf, and had been searched again on arrival at Camp Liberty.
They also complained that they had not been allowed to bring many of their vehicles, household items and personal possessions with them.
"This process is a humiliating and degrading treatment,'' Bahzad Saffari, 50, told AP news agency.
"We are very frustrated and have been going through this harassment for more than 24 hours now. The camp looks horrible - it is totally different from the photos that were provided to us.''
In a statement, the National Council of Resistance of Iran - a umbrella group which includes the PMOI, which the US designates a terrorist organisation - complained that the new camp failed to meet "the most basic international humanitarian standards and human rights standards" and was in essence "nothing but a prison".
It said no additional transfer would take place until certain minimum assurances were made - in particular the removal of Iraqi armed forces from the camp.
But the UN envoy to Iraq, Martin Kobler - who was present when the exiles arrived - welcomed their move.
"It is clear that for Camp Ashraf residents, there is no future inside Iraq,'' Mr Kobler told reporters. "It is better for them if they find a relocation outside the country in a third country.''
Despite a UN appeal, only a handful of exiles have been offered asylum in UN member states, they say.