CAIRO (AP) — U.N. human rights experts urged Egypt on Thursday to halt the execution of six men, sentenced to death over killing a policeman, saying that their trials were "flawed" and "did not meet international standards of fairness."

The U.N statement comes after Egypt's top appeals court upheld the death sentences against the men, charged with killing the guard of a judge who was on a panel of judges in the trial of former Islamist President Mohamed Morsi, in which he was sentenced to 20 years on charges of killing protesters during his reign.

The men were arrested among others in 2014, less than two weeks after the guard was killed. Egypt's Interior Ministry accused them of belonging to the outlawed Muslim Brotherhood group.

Three of the men appeared on TV following their arrest and in the footage, confessed to carrying out the attack. But rights groups have said the testimonies were coerced through torture.

"The defendants recanted the confessions made under torture, and asserted that the severity of torture allegedly made them consent to memorize police stories that confirm the charges against them," the Egyptian Initiative for Personal Rights said in a statement earlier this month.

U.N rights experts expressed "deep concern" over the convictions of the men based on "forced confessions" which were later retracted and demanded clarification from Egyptian authorities.

"This is in clear violation of Article 1 of the Convention against Torture, to which Egypt is a party," they said, adding that supporting evidence used against the men, as well as testimonies from state security members, showed major inconsistencies.

International watchdogs have repeatedly voiced their concern over human rights abuses in Egypt, allegations Egypt routinely denies or attributes to isolated instances.