(Adds U.S. comment in paragraphs 4 and 5)
CAIRO, Dec 23 (Reuters) - Hundreds of Egyptians protested in central Cairo on Monday against a court ruling that sent three leading secular pro-democracy campaigners to jail, witnesses said.
Raising a banner reading "Freedom for all detainees", the protesters chanted against the military-backed government, calling army chief General Abdel Fattah al-Sisi "a dog".
A court on Sunday handed out three-year jail sentences to Ahmed Maher, Ahmed Douma and Mohamed Adel, symbols of the uprising that toppled President Hosni Mubarak in 2011, for protesting without permission and assaulting the police.
The European Union and the United States urged Egypt to reconsider the sentences. In Washington, the State Department said it was deeply concern with the "worsening climate for freedom of assembly and peaceful expression in Egypt."
"We believe that the verdicts issued Dec. 22 do not contribute to an open electoral environment or a transition process that protects the universal rights of all Egyptian citizens, and therefore should be reviewed," State Department spokeswoman Jen Psaki said in a statement.
Egypt's rulers passed a law last month banning protests not authorised by police in an attempt to end demonstrations by Islamists demanding the reinstatement of elected President Mohamed Mursi, who was removed by the army in July.
The new law prompted more protests led by liberal activists including Maher, Adel and Douma.
The court ruling fined the three activists 50,000 Egyptian pounds ($7,200) each and ordered them to be put under police supervision for three years after their jail terms end.
"Why is this government so scared of us? Down, down with the military rule," their supporters chanted during Monday's march, which the police took no action to prevent.
One of the demonstrators, Louai Mohamed, said the march was organized in response to the jailing of the activists. "We will continue our protests and the revolution will continue," he said.
Sisi, who overthrew Mursi following mass protests against his rule, still enjoys wide public support, but his fierce crackdown on Mursi's Muslim Brotherhood and now the punishment of his secular critics has eroded his popularity.
The government is pursuing a political transition plan that will include a mid-January vote on a new constitution, followed by presidential and parliamentary elections. ($1 = 6.9175 Egyptian pounds) (Reporting by Ayman Abdel Maged, Writing by Yasmine Saleh; Editing by Alistair Lyon and Christopher Wilson)