BAGHDAD  Two synchronized suicide car bombings struck at the heart of the Iraqi government here on Sunday, severely damaging the Justice Ministry and provincial council complexes, leaving a scene of carnage that raised new questions about the government’s ability to secure its most vital operations.

The bombers apparently passed through multiple security checkpoints before detonating their vehicles within a minute of each other, leaving at least 155 dead and about 500 wounded strewn across crowded downtown streets. Blast walls had been moved back off the road in front of both buildings in recent weeks.

It was the deadliest coordinated attack in Iraq since the summer of 2007 and happened just blocks from where car bombers killed at least 122 people at the Foreign and Finance Ministries in August, in the continuation of a focused attempt by insurgents to strike at the government’s most critical functions.

For months, Prime Minister Nuri Kamal al-Maliki, who is seeking another term as Iraq prepares to hold national elections in January, has painstakingly tried to present Iraq as having turned a corner on the violence that threatened to tear the country apart in 2006 and 2007.