Former US Senator Tom Daschle has launched a scathing attack on Nepal's king, who seized power in February.
The king says he is rooting out corruption
Speaking in Kathmandu after talks with King Gyanendra, Mr Daschle called for the release of ousted former PM Sher Bahadur Deuba, jailed for corruption.
Mr Daschle said all political prisoners must be freed and urged the king to scrap a controversial corruption body.
As he made his statement, security forces re-arrested a prominent student leader, Gagan Thapa.
A senior police source told the BBC evidence was being gathered to lay charges against Mr Thapa, detained for several weeks earlier this year, in a special court.
Mr Daschle led the Democrat Party in the US Senate for 12 years until losing his seat last November.
He stressed he was not speaking for the US administration, which has called on the king and political parties to work together and is reviewing military assistance to Nepal.
The former senator laid into all sides in Nepal's crisis at a news conference in the capital.
He said the parties sidelined by the king should remove what he called corrupt people from their ranks and offer a blueprint for change.
He urged the Maoist guerrillas to end abduction, extortion and violence.
But the BBC's Charles Haviland in Kathmandu says Mr Daschle's most blistering criticisms were aimed at the royal palace.
Pointedly, the former senator said, corrupt people and convicted criminals should have no place in the royal-led government - a reference to a minister once jailed for attempted murder, our correspondent says.
Mr Deuba refused to recognise the commission
The powerful anti-corruption commission which sentenced Mr Deuba to two years in jail on Tuesday was set up by the king in February.
Nepalese opposition parties have condemned the sentence as an act of political vendetta.
Mr Daschle said the authorities must release all political prisoners, including the former prime minister.
Asked if he thought the monarch would act on all this, Mr Daschle said: "I wish I could be more hopeful that his majesty heard and was willing to act."