Egypt has rejected US criticism over a court decision on Thursday to turn down an appeal against conviction by opposition leader Ayman Nour.
Ayman Nour was convicted of forging signatures on a petition
Mr Nour was a distant runner-up in last year's presidential election but was later convicted of forgery and jailed for five years.
The US state department called the decision a "miscarriage of justice" and a setback for democracy.
Mr Nour's supporters said it is likely that he would serve his full term.
Egypt's foreign ministry said on Friday it was "astonished" at the US statement , which "implied an affront to the rulings and independence of the Egyptian judiciary".
State Department spokesman Sean McCormack said: "The Egyptian government's handling of this case represents both a miscarriage of justice by international standards and a setback for the democratic aspirations of the Egyptian people."
The court verdict and US criticism came as hundreds of members of the main opposition party, the Muslim Brotherhood, were arrested in Cairo following street protests.
Mr McCormack said these developments "raise serious concerns about the path to political reform in Egypt".
Mr Nour maintains that his conviction is politically motivated and intended to remove him from public life.
His wife, Gameela Ismail, told the Associated Press news agency the decision not to allow an appeal reflected badly on the government of Egyptian President Hosni Mubarak.
"This verdict proves for the 1,000th time that Mubarak and his regime are controlling the judicial, executive and legislative authorities in Egypt - the bodies whose independence Nour was fighting for."