Two attacks coordinated one minute apart of each other killed nine members of an elite police commando unit just after 12pm (0900 GMT) in the Dora district of the capital.
Earlier, a similar attack in the same area killed 16 members of the same unit.
A police official said the policemen were riding in a truck. Earlier, police had reported that five civilians were caught in the blast and killed.
Twenty-one people were also wounded in the earlier attack, police sources added.
The attacks came on the heels of a series of car bombings and shootings which killed 150 people on Wednesday.
Late on Wednesday, al-Qaida in Iraq leader Abu Musab al-Zarqawi declared all-out war on Iraq's Shia community and any who supported the government of Prime Minister Ibrahim al-Jaafari.
He also warned the Sunni community not to participate in an upcoming referendum.
In other attacks reported in Iraq on Thursday, at least two policemen were killed and four wounded in a bomb attack in the northern Iraqi oil-rich city of Kirkurk, police said.
"A bomb exploded on the side of the road at 7.45 (0435 GMT) this morning in al-Askari neighbourhood completely destroying a police patrol vehicle," police Captain Mohammed Aden said.
Three of those wounded were in a serious condition, he added.
Meanwhile, Iraqi journalist Walid Khalid told Aljazeera three Shia pilgrims were killed by unidentified assailants as they headed towards the southern city of Karbala.
In the Shula district of western Baghdad, police reported finding three persons, apparently shot to death. They had not yet been identified.
In al-Madain, southeast of Baghdad, a central marketplace came under a barrage of rocket-propelled grenades on Wednesday evening, police said.
Two civilians were killed and 75 others wounded, 20 of whom were reported in critical condition.
They were transferred to Baghdad hospitals, Khalid told Aljazeera.