The FBI has identified similarities between two of the three recent bombings in Iraq.
Chemical tests found similar munitions were used in the bombing of the Jordanian Embassy in Baghdad on August 7th and the attack on the United Nations headquarters there 12 days later.
Results from tests on last Friday's bombing of the Imam Ali shrine in Najaf should be available in a few days.
Top FBI counter-terrorism officials said the explosives used in the two similar bombings could be widely available in Iraq.
Presence of similar munitions do not necessarily prove the bombings are linked to the al-Qaida terrorist network, loyalists to the Saddam Hussein regime or some other group.
Nineteen people died in the embassy bombing and 23 at UN headquarters.
The Najaf mosque bombing killed up to 125, including leading Shiite cleric Ayatollah Mohammed Baqir al-Hakim.