Almost two-thirds of Americans disagree with the decision by President Barack Obama's administration to try the suspected 9/11 mastermind in a civilian court, a poll showed Monday.

Sixty-four percent of those surveyed said Khalid Sheikh Mohammed should be tried in a military court, while only 34 percent agreed with Obama that the civilian judicial system was the best way forward, the CNN poll said.

Attorney General Eric Holder announced on Friday that Sheikh Mohammed and four suspected co-plotters of the September 11, 2001 attacks that killed nearly 3,000 people would be tried in New York in a civilian court.

Sixty percent of those questioned in the CNN poll agreed that Sheikh Mohammed should be brought to the United States to stand trial, while 37 percent opposed the move.

There was overwhelming support for Holder's announcement that prosecutors would seek the death penalty for Sheikh Mohammed.

Seventy-eight percent of those polled said they thought he should be executed if found guilty, almost a quarter of whom said they didn't normally support capital punishment.

More than a third of the 1,014 Americans questioned by CNN in the weekend poll, 34 percent, said they didn't think Sheikh Mohammed would receive a fair trial if brought to a US civilian court.

Friday's announcement, key to Obama's attempts to try and shutter Guantanamo Bay by January, was blasted by families of the victims of the September 11 attacks and the president's political opponents.

Former New York mayor Rudolph Giuliani said it was as an "unnecessary risk" to New York's security that would give an "unnecessary advantage" to the accused.