Iraq says it is extending the current security drive beyond Baghdad to areas outside the capital.
The drive is now under way in Mosul in the north
Efforts to bring the security plan to the northern city of Mosul began on Tuesday, officials said, and Baghdad's outskirts would also be targeted
Officials have expressed optimism about reduced sectarian violence in Baghdad, and have decided to ease the curfew.
But the US military said car bombs were a major concern and nationwide the scale of violence was worse than hoped.
On Tuesday, gunmen abducted 22 shepherds from the desert near the central city of Karbala.
Iraqi government spokesman Ali al-Dabbagh said Operation Fardh al-Qanoon was now in place in Mosul.
"The efforts are now extending beyond Baghdad to provide peace and security to other provinces," he said.
Mr Dabbagh said security improvements in Baghdad meant that from Wednesday the daily curfew had been eased by three hours and now applied between 2200 and 0500 (1800 GMT to 0100 GMT).
"Security is improving and we now also plan to lift concrete barriers in some areas to facilitate movement of people," he said.
The US has this year brought in about 30,000 more troops to bolster the security drive.
US military spokesman Maj Gen William Caldwell said sectarian killings in the capital were down 27% in March compared to February.
But he said car bombings were still a major concern, with hundreds dead in the past week.
"There has been a drop in overall casualties within Baghdad," Gen Caldwell said.
But he added: "When you look overall at the country at large you have seen... not a great reduction that we had wanted to see thus far."
US President George W Bush and Iraqi Prime Minister Nouri Maliki discussed the situation by videoconference on Monday.
Mr Bush reportedly expressed concern that two unexploded suicide vests had been found near a rubbish bin inside Baghdad's security Green Zone.
An Iraqi official said Mr Maliki told Mr Bush this was expected as "some politicians are involved in terrorism".
The Shia shepherds who were abducted had travelled from Karbala to greener desert around Amariyah in Sunni-dominated Anbar province.
One witness said: "Six of us were able to flee in our pickup but unfortunately they kidnapped 22 friends of mine and stole our sheep."
Separately, Radical Shia cleric Moqtada al-Sadr reportedly fired two senior members of his movement who failed to walk out of a dinner once the US military chief Gen David Petraeus arrived.
One of the men, Salam al-Maliki, denied they had been sacked but the other, Qusai Abdul-Wahab, confirmed it. Both were representing the Sadr movement in parliament.