Bombs exploded across Baghdad on Tuesday, killing 16 people and wounding dozens, two of the blasts striking the crowded Shi'ite slum of Sadr City, security officials said, Reuters reported.
In Iraq's usually quiet Anbar province, the country's largest, a rare two-day vehicle ban was imposed across the vast desert region after bombings in the provincial capital Ramadi.
The first Sadr City bomb, apparently targeting day labourers, killed four people and left 39 wounded, said Baghdad security spokesman Qassim al-Moussawi.
Another bomb in the same area of northeastern Baghdad killed three civilians and wounded 15. The slum was once a haven for gunmen loyal to anti-American cleric Moqtada al-Sadr, but the militia has now been largely disbanded and splintered.
In Husseiniya, just north of Baghdad, a series of blasts in a popular market killed five people and wounded 28, police said.
U.S. combat troops pulled out of Iraqi cities and towns on June 30, implementing the first stage of a security pact that requires all troops to leave by the end of 2012, raising doubts about whether Iraqi forces are ready to handle security.
A roadside bomb killed two civilians and wounded 13 others all from the same extended family as they made their way to a funeral in central Baghdad on Tuesday. And a car bomb exploded near a vegetable market, killing two civilians and wounding six others in south Baghdad's Doura district, police said.
Many Iraqis doubt whether their own forces can protect them against militants without backing from U.S. firepower.
But in an interview with Reuters on Monday, the commander of Iraqi forces in Baghdad, Major-General Abboud Qanbar, said he had not once had to call on U.S. troops now stationed on the city's outskirts to help keep security.
A major Shi'ite pilgrimage that drew millions to the Baghdad district of Khadhimiya, a favourite past target of Sunni Islamist militants, went by without any major bomb attacks over the weekend, he said.
Militants are likely to step up attacks to test Iraqi security forces ahead of national elections scheduled for January, officials say. Some politicians will try to intimidate rivals or show the government is failing on security by backing militant groups who plant bombs, Qanbar said.
"This year is such an important year: it is the last chance for the enemy," he said.
"This is also an election year. Politicians will use attacks to try to gain advantage over rivals," he added.
Officials declared a state of emergency in Ramadi and police said a province-wide vehicle ban had been imposed after two bomb attacks on Tuesday. The previous day, an explosion killed two policemen.
A suicide bomber in a moving car and a bomb in a parked car detonated almost simultaneously near a group of restaurants, killing three people, police said.
During a state of emergency more police are deployed, and they conduct greater security checks.
Anbar was once overrun by Islamist militants such as al Qaeda, but a mostly Sunni Muslim anti-insurgent movement started by the province's tribal leaders in 2006 was decisive in routing them. The province has remained relatively calm since then, but has witnessed a rise in attacks in recent months.
Violence has fallen sharply across Iraq, but militant groups are still capable of carrying out frequent bomb attacks.