The comments by Prachanda, the rebel commander, came after James F. Moriarty, the US ambassador to Nepal, said on Saturday that the US would not aid those involved in violence.
Moriarty, speaking to journalists in Kathmandu, said: "If the Maoists continue to use violence and then enter the government, our law says we can't supply assistance to those who support [terrorism]."
Prachanda responded that the US was trying to create "an atmosphere of suspicion" and "stop a peaceful atmosphere from building up".
"I am not surprised with the comments by the ambassador to Nepal, because he does not want peace in Nepal," he told Nepal's state-owned Rising Nepal newspaper on Sunday.
"He seems very unhappy and restless over the political development and is trying to dismantle the harmony that is about to develop among the political parties," he added.
At the present the US provides Nepal with $45 million a year in development, education and health aid.
In the past, the US had given Nepal's government millions of dollars in military aid to fight the rebels, but suspended the funds after Nepal's monarch, King Gyanendra, seized absolute power last year.
The rebels have waged a decade-long war to seize control of Nepal, which killed more than 13,000 Nepalis.
They supported the massive, often violent street protests against King Gyanendra's rule earlier this year in which at least 18 people died.
Since then, the group have announced they will join an interim government to be formed along with the country's main political parties after the King relinquished power.
The interim government, which will eventually create a new permanent constitution, is to replace the current national parliament as well as the Maoists' "people's government", which rules territory they control.