U.S. troops blew up two cars Tuesday inside the heavily fortified Green Zone after dogs indicated explosives were inside the vehicles that were used in the motorcade of the parliament speaker, an adviser to parliament said.

In what could signal a major security breach, the explosives were found and detonated near the Convention Center, where parliament meets and government officials hold news conferences, Wissam al-Zubeidi said.

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The armored cars were used as part of the convoy for Parliament Speaker Mahmoud al-Mashhadani, al-Zubeidi said. One of the vehicles was regularly used by al-Mashhadani's son. The speaker is a Sunni Muslim.

In the past, several car bombs have exploded at the Green Zone gates, but very few such attacks have occurred inside the fortress-like region on the west bank of the Tigris River. It is home to the Iraqi president, government, parliament, as well as the U.S. and British embassies.