CAIRO — A night of street fighting between hundreds of Muslims and Christians left at least 12 people dead and two churches in flames on Sunday in the latest outbreak of sectarian tensions in the three months since the revolution that ousted President Hosni Mubarak.

By lifting the heavy hand of the Mubarak police state, the revolution unleashed long-suppressed sectarian animosities that have burst out with increasing ferocity, threatening the recovery of Egypt’s tourist economy and the stability of its hoped-for transition to democracy.