A parked car bomb exploded in a bustling section of downtown Baghdad early Wednesday, killing four people and wounding 15 others, police said, in the third consecutive day of morning rush hour blasts. Another car bomb struck the Shi'ite-dominated neighborhood of Shaab in north Baghdad, but there were conflicting casualty reports from that attack. The US military said seven people were injured. Iraqi police said five people were killed, and 12 wounded, including three teachers and two students who were on their way to a nearby school. There was no way to immediately reconcile the differences. In the face of heightened violence in the capital, the Iraqi military said it was taking measures to curb "the increasing number of terrorist attacks" in the capital. Military spokesman Maj. Gen. Qassim al-Moussawi said the measures would include stepped up intelligence gathering and pre-emptive strikes on suspected extremists. The blast in downtown Baghdad occurred around 9:30 a.m. (0630 GMT) off Nasir Square in the heart of the city - a busy neighborhood of shops, pharmacies and photography stores. The car bomb in Shaab went off near the Baidha secondary school. Earlier Wednesday, another roadside bomb exploded in Shaab, wounding seven people including three policemen. officials said. They spoke on condition of anonymity because they were not authorized to release the information. The attacks follow two days of morning rush hour blasts in Baghdad that have killed more than 30 people and wounded some 70 others. The recent spate in bombings has occurred despite security gains in recent months that have seen violence drop sharply in the capital. Many of the attacks have targeted Iraqi police and army patrols, as well as government officials heading to work and commuters. In the first nine days of November, there were at least 19 bombings in Baghdad, compared with 28 for all of October and 22 in September, according to an Associated Press tally. The rise in attacks also come as US and Iraqi officials try to hammer out a final agreement on a security deal that would keep US troops in Iraq until the end of 2011. The security pact has drawn sharp criticism, especially from within the majority Shi'ite community. The current UN mandate authorizing the US presence in Iraq expires at the end of December. Without a security agreement or a new UN mandate, the US military would have to cease operations in Iraq. In an attempt to derail the pact, 10 Iraqi insurgent groups have agreed to ramp up attacks against US and Iraqi forces, according to the SITE Intelligence Group, an Internet monitoring service. But it remains unclear who is responsible for the recent attacks in Baghdad. Meanwhile, unidentified gunmen in the volatile northern city of Mosul killed two sisters from a Christian family as they were waiting in front of their house for a ride to work, police said. The women's mother was injured in the attack. The attack in Mosul - an ethnically mixed city of Kurds, Christians and Arabs - comes after about 13,000 Christians fled the city last month in the face of threats and attacks from extremists. Some families have started returning to the city, although tensions linger. Mosul has seen a spike in violence in recent months as the ethnic groups vie for power, and US troops and Iraqi security forces continue to wage an intense battle with insurgents in the city.