BAGHDAD Six bombs rocked Shiite neighborhoods of Baghdad today, killing 34 people and wounding more than 90 in a dramatic escalation of violence as the U.S. military is thinning out its presence before a June 30 deadline to pull combat troops out of the cities.

Angry survivors hurled stones at Iraqi soldiers at the site of one of the blasts in Sadr City after troops fired shots in the air to disperse crowds of people trying to care for the injured, witnesses said.

No group claimed responsibility. But a U.S. military spokesman said the attacks appeared to be a coordinated assault by al-Qaida, saying the nature of the targets was consistent with past attacks.

The deadliest blast occurred in a market in western Baghdad where two car bombs exploded almost simultaneously, killing 12 people and wounding 29 others, an Iraqi police official said.

Burned hulks of cars and twisted metal were scattered across the marketplace, as Iraqi soldiers and police officers surrounded the bombing site, driving off onlookers and journalists.

U.S. officials insist that violence has fallen by 90 percent since the high point in 2007, but a recent uptick in attacks has raised concern that extremists may be regrouping.

Also today, the U.S. military announced that a U.S. soldier was killed in action the day before in Diyala province, where insurgents remain active.

It was the first combat death suffered by U.S. forces in Iraq since March 16, when a soldier was killed by a roadside bomb in Baghdad.