Clinton also said Cambodia could find creative means of repaying more than $400 million in debt incurred during the Lon Nol regime.
Ban said he felt the government was “committed to completing the process” of the court and that Cambodians seek and deserve justice.
The UN may be pushing for more funding at the tribunal, which has struggled financially all year.
If accepted by the Supreme Court Chamber, the sentence would be a large increase to the 19 commuted years Duch received in July.
The question of reparation remained high on the agenda Thursday in Kampong Cham.
There are also sentiments here that the tribunal is already holding the wrong people.
Lemonde joined the tribunal in the office of co-investigating judges in 2006.
Defense teams and prosecutors both have 30 days to appeal the closing order, which came after three years of investigation.
Their trial is expected to start in the first half of next year. The suspects deny the charges against them.
The film won the Special Jury Prize at the Sundance film festival in January and has been released in the US, Europe and Asia.
Cabinet Minister Sok An on Tuesday urged representatives from 30 donor countries to consider more funding for the Khmer Rouge tribunal.