US pledges $450m to back Egypt's faltering economy
Mr Kerry's comments came after talks with President Mohammed Morsi.
He urged Mr Morsi to ensure April polls were free, fair and transparent.
His visit came amid unrest over a trial of alleged perpetrators of football riots last year. Hours after Mr Kerry left, a policeman was killed in the city of Port Said, the army said.
A military officer was among several hundred wounded in the unrest, as police dispersed a crowd of about 5,000 protesters with tear gas.
The battle continued into the night and at one point Egyptian soldiers intervened by forming a line between protesters and police, witnesses said, BBC informs.
Mr Kerry's departure from Cairo was delayed because hundreds of al-Ahly football supporters blocked the road to the airport demanding justice over the 2012 Port Said riot in which 74 fans died.
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