* Violence is worst sectarian strife since Mubarak toppled
* Containing strife another challenge for military rulers
(Increases death toll to 13, wounded to 140)
By Yasmine Saleh
CAIRO, March 9 (Reuters) - Thirteen people were killed in violence between Egyptian Christians and Muslims, the health ministry said on Wednesday, as sectarian tensions that appeared to evaporate in the country's revolution resurfaced.
The health ministry said 140 people were wounded, state media reported.
The violence in Cairo on Tuesday night was the worst outbreak of sectarian strife since President Hosni Mubarak was swept from power on Feb. 11 by a mass uprising characterised by solidarity between Christians and Muslims.
It was not immediately clear how many of the dead were Christian or Muslim. The violence erupted following a protest by Christians over an arson attack on a church in Helwan south of Cairo.
The strife represents another challenge to the military rulers to whom Mubarak handed power, and who made restoring law and order a top priority.
Petrol bombs and rocks were thrown, witnesses said. At least one of the dead was a Christian who had been struck in the back by a bullet, but it was unclear who fired it. The army fired into the air at one point to disperse protesters.
The health ministry earlier put the death toll at four.
Christians protesting over the attack on the church had blocked a main highway south of Cairo and violence started after Muslims, who wanted to pass through, clashed with the protesters, a security source said.
Coptic Christians make up about 10 percent of Egypt's population of 80 million.
Islamists on Tuesday protested outside the prime minister's office over the case of two women who they believe are being held against their will in churches after converting to Islam.
Writing by Tom Perry, editing by Peter Millership and Michael Roddy