"My opinion is that the US should establish some communication with the Maoists. The people of Nepal have accepted them as political players," Carter told journalists at the end of a four-day visit to Nepal.

The US remains highly critical of the Maoists, despite the fact they signed a landmark peace deal last year and entered government in April.

Earlier this week the US ambassador to Nepal James Moriarty said that the ultra-leftists' "addiction to violence, extortion and intimidation continues unabated."

During his visit, Carter met with Prachanda, the Maoist leader whose nom-de-guerre means "the fierce one."

The 82-year-old former president admitted he was worried about the activities of the Young Communist League (YCL), the Maoist youth wing that has frequently been accused of using mafia-like tactics.

"I am still concerned about some of the activities of the YCL. My hope is that they will be corrected," Carter told reporters at a hotel in the capital.

"I have expressed my concern to him (Prachanda) and he has assured me he will do whatever possible to correct the problem," Carter said.

The former president's Carter Centre has been invited to provide election monitors in crucial polls planned for November.

The vote will elect a body that will rewrite Nepal's constitution and decide the future of the sidelined monarchy.

The US embassy in Kathmandu have been at pains to emphasise that Carter is visiting as a private US citizen.

Meanwhile, Nepal was urged on Friday to investigate "thousands" of disappearances during the 10-year Maoist rebellion.

Human Rights Watch (HRW) and the International Commission of Jurists said the government should act on a Supreme Court order to set up an inquiry.

"Nepal's new government has promised to find the truth and ensure justice for disappearances, but has been slow to make good on these pledges," HRW Asia director Brad Adams said in a statement.