Senior Iraqi weapons scientists who are in hiding from US troops have contacted former UN inspectors to discuss giving themselves up.
But they fear they will be jailed if they do not tell their interrogators what they want to hear.
One of the ex-inspectors contacted, David Albright, a Washington-based expert on nuclear proliferation, said the fall of president Saddam Hussein's regime had not brought an end to the climate of fear hanging over Iraqi scientists.
"A sizeable group from the nuclear program want to cooperate with the US, but they don't want to be detained if they turn themselves in," Albright said. "They worry that if they go in, the US investigation is going to focus on one thing: `If you tell us where the weapons are we'll treat you kindly.' But they may genuinely know nothing about it."
Albright said that all the Iraqis he had talked to denied knowledge of recent weapons programs, but he added that that was hardly surprising as they were talking over open telephone lines, and might want to use what knowledge they had as a bargaining chip for better treatment.
Albright, who runs the Institute for Science and International Security, said that after the fall of the regime, he had contacted some of the former Iraqi scientists he had met during earlier UN inspections. Some, including a senior Iraqi nuclear scientist, had sought him out.
The nuclear scientist had been found by journalists but said he would only to talk to them if they could put him in touch with Albright. He said he knew of other former inspectors who had also been contacted by fearful Iraqis.
The scientists, having lived for so long in fear of reprisals if they spoke about Iraqi weapons programs, are also unconvinced that the threat from the ousted regime has passed.
"We're worried that if they are seen as cooperating they could be targeted by Saddam loyalists as collaborators," Albright said.
"The regime was always ready to punish families. We're talking about fears here, but given the security problems in Baghdad they're not unfounded," he said.
Another former UN inspector, Stephen Black, said: "No one has said to these people that there are not going to be trials for people who had been secretly involved in programs to make weapons of mass destruction. So why should they cooperate?"
"This is a little bargaining game. They have something of use to us. They are looking for ways to maintain their nice lifestyle that they had before," Black said.
He added he had not personally been approached by any Iraqi scientists. US-led forces in Iraq have so far failed to find any conclusive proof that Saddam had developed banned weapons in recent years.
Former leaders from the regime already in custody have also denied such weapons programs existed.
Pentagon officials said on Tuesday that experts are examining an Iraqi trailer suspected of being used as a mobile laboratory for chemical weapons.