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A top U.S. military spokesman in Iraq said Sunday that the use of a type of lethal roadside bomb thought to come from Iran declined last week after a sharp increase earlier this month.

Ten days ago, Gen. David Petraeus, the top U.S. military commander in Iraq, noted a sharp rise in the use of explosively formed penetrators. The sophisticated roadside bombs, which fire slugs of metal that can pierce armor, are thought to come from Iran and to have killed hundreds of U.S. soldiers.

At a news conference Sunday, Rear Adm. Gregory Smith said the use of EFPs has returned to “normal levels” after a brief increase in the first weeks of January. He couldn’t explain the increase, nor could he say whether Iran was behind the delivery of the weapons to Iraq.

However, Smith said there is evidence that Iran continues to support Iraqi Shiite Muslim groups.

“We continue to see a negative influence by Iran,” Smith said. “We clearly see their intent of training and financing continues.”

Sunday’s news conference, which summarized the U.S.-led coalition’s efforts against Al Qaeda in Iraq in the past year, was held as a teenage suicide bomber killed the leader of a Sunni group allied with the U.S. near Fallujah and three others. The so-called Awakening Councils, predominantly Sunni, have been a key part of the U.S. strategy against Sunni Islamic extremists in the past year, and there have been increased attacks on them in recent weeks.

Smith also said that nearly half of foreign insurgents in Iraq come from Saudi Arabia. Others have come from Libya, Yemen, Syria and even a few from France, he said.