Baghdad, Iraq ? At least 20 people were killed Tuesday in a string of bombings in the center of Baghdad, as more American soldiers patrolled the streets of the capital in a make-or-break bid to quell sectarian violence.

Nearly 60 people were wounded in the blasts, police said. The explosions began when three bombs went off simultaneously near the Interior Ministry in central Baghdad, killing 10 people and wounding eight, police Lt. Bilal Ali Majid said.

Two more bombs ripped through the main Shurja market, also in central Baghdad, killing 10 more civilians and wounding 50, police Lt. Mohammed Kheyoun said.

At least 13 other people were killed or found dead Tuesday, most in the Baghdad area, where tension between Sunnis and Shiites runs the highest.

The violence underscores the security crisis facing Baghdad, which prompted American commanders to send more U.S. soldiers to the capital in a renewed bid to curb sectarian killings and kidnappings.

U.S. officials said the latest phase of the security operation was launched Monday “to reduce the level of murders, kidnappings, assassinations, terrorism and sectarian violence in the city and to reinforce the Iraqi government’s control of Baghdad.”

A U.S. statement said about 6,000 additional Iraqi troops were being sent to the Baghdad area, along with 3,500 U.S. soldiers of the 172nd Stryker Brigade Combat Team and 2,000 troops from the U.S. 1st Armored Division, which has served as the theater reserve force since November.

More heavily armed U.S. soldiers were seen Tuesday on the streets of Ghazaliyah, one of the areas targeted in the first stage of the stabilization effort.