Brigadier Jibri Rajoub, security adviser to Yasir Arafat, on Wednesday said the Americans has stopped going to the Gaza Strip since a US diplomatic vehicle was hit on 15 October by a roadside bomb.
"The Americans stopped their involvement waiting for the results of our investigation. This is blackmail," Rajoub said.
The stoppage of visits by the Americans has hit aid programmes for the Palestinians.
"I think the Americans are using this…isolated case in order not to be involved, in order to blackmail the Palestinian Authority," Rajoub said.
The US dismissed the accusation, reiterating its commitment to the peace process and its aid programmes and complained the Palestinians could do more to arrest the killers of the three security guards.
"Comments like that are ridiculous," State Department spokesman Richard Boucher said.
"We have seen some cooperation on the investigation, but we think that cooperation needs to be further increased," Boucher added.
No group has claimed responsibility for the 15 October attack that has further complicated relations between the Palestinians and Washington.