BAGHDAD (AP) — A wave of explosions struck two Shiite neighborhoods in Baghdad on Thursday, killing at least 27 people and intensifying fears that insurgents are stepping up attacks after the U.S. troop withdrawal that was completed last month.

The attacks began with the explosion of a bomb attached to a motorcycle near a bus stop where day laborers gather to look for work in the Sadr city neighborhood. One of those who witnessed the attack said it filled the area with thick black smoke.

"People have real fears that the cycle of violence might be revived in this country," said Tariq Annad, a 52-year-old government employee who lives nearby.

That attack was followed by the explosion of a roadside bomb. Police found a third bomb nearby and defused it.

The two Sadr City blasts killed 12 people, according to police and medical officials.

Less than two hours later, two explosions rocked the Shiite neighborhood of Kazimiyah in the north of the capital, killing 15 people.

Officials said the Kazimiyah blasts occurred almost simultaneously, with at least one caused by a car bomb.

Hospital officials confirmed the causalities from the four blasts, which included more than 60 wounded.

The officials spoke on condition of anonymity because they were not authorized to release the information.

The Baghdad military spokesman, Maj. Gen. Qassim al-Moussawi, said the aim of the attacks is "to create sedition among the Iraqi people." He said it was too early to say who was behind the bombings.

Coordinated bombings, particularly those targeting Shiite areas, are the hallmark of Sunni militants linked to al-Qaida.

Thursday’s attacks were the deadliest in Baghdad since Dec. 22, when a series of blasts killed 69 people in mostly Shiite neighborhoods. An al-Qaida front group in Iraq claimed responsibility for those attacks.

Iraqi leaders have warned of a resurgence of Sunni and Shiite militants and an increase in violence following the departure of U.S. troops.

The early morning blasts followed deadly attacks Wednesday that targeted the homes of police officers and a member of a government-allied militia. Those attacks, in the cities of Baqouba and Abu Ghraib outside Baghdad, killed four people, including two children, officials said.

The latest violence comes as Iraqi politicians remain deadlocked in a festering political crisis that threatens to re-ignite simmering sectarian tensions in the country.

Prime Minister Nouri al-Maliki’s government, dominated by Iraq’s majority Shiites, issued an arrest warrant for the country’s top Sunni politician last month. The Sunni official, Vice President Tariq al-Hashemi, is currently holed up in Iraq’s Kurdish north — effectively out of reach of state security forces.

Al-Maliki’s main political rival, the Sunni-backed Iraqiya bloc, is boycotting parliament sessions and Cabinet meetings to protest what they say are efforts by the government to consolidate power and marginalize them.

———

Associated Press writers Qassim Abdul-Zahra and Adam Schreck contributed to this report.