Gunmen in the Iraqi capital Baghdad have killed at least 40 people at a fake police checkpoint, in an apparent sectarian attack against Sunni Muslims.
Women and children were among the casualties of the Jihad attack
Police say Shia militants stopped cars in the western Jihad district, separated Sunnis and shot them.
Later, at least 25 people died when two car bombs exploded near a Shia mosque in the capital, police said.
There has been an upsurge in sectarian violence in Iraq in recent months, raising fears of a civil war.
Sunni Arabs say government-backed Shia militias are behind many of the attacks. But officials have denied any involvement.
The BBC's Jonny Dymond in Baghdad says the style and scale of Sunday morning's incident was breathtaking.
Witnesses said Shia militiamen entered Jihad and set up roadblocks.
Drivers were reportedly pulled from their cars and their identity cards inspected.
Any Sunni Muslims identified were then separated from the rest and killed.
"They also went into certain Sunni houses and killed everyone inside," said a witness quoted by AFP news agency.
Call for calm
Another told the Associated Press news agency: "They came and started shooting. One of my relatives tried to help but was also shot while doing so. What crime have my people committed, I ask?"
Officials say they are getting reports of drive-by shootings in the area, and the number of deaths is expected to rise.
Security forces have sealed off the area and imposed a curfew, in an effort to prevent revenge attacks.
Officials said the shooting could be in retaliation for a car bomb that killed at least two people at a nearby Shia mosque on Saturday.
Radical Shia cleric Moqtada Sadr appealed for calm following the shootings.
Mr Sadr calls on Sunnis and Shias to "put our hands together for the sake of Iraq's independence and stability", AP quoted him as saying.
Mr Sadr's Mehdi Army militia was suspected of involvement in the attacks, but Mr Sadr's office denied any responsibility.
In more bloodshed hours after the shootings, Baghdad's northern Kasra district was rocked by the double car bomb attack.
Police said the vehicles exploded in a market place near the local Shia mosque, killing at least 25 people and wounding dozens of others.
Our correspondent says it may have been revenge for Sunday morning's attack or it may have been planned beforehand.
But he says whatever the motive, the impact is the same: Iraq's capital is tearing itself apart.
A wave of sectarian killings has engulfed many parts of Iraq - especially Baghdad - since the bombing in February of a revered Shia shrine in Samarra.
In other violence on Sunday, an Iraqi army intelligence officer was shot dead in Karbala, south of Baghdad.
Several policemen and civilians were also killed in separate attacks around the country.
Meanwhile reports say three Egyptians held hostage in Iraq have been released.
It is not known when the men, who have not been identified, were abducted.