BAGHDAD, Iraq (CNN) — Iraqi Prime Minister Nuri al-Maliki is telling the United States and Iran to keep their fight out of Iraq.

Al-Maliki said he believes Iran is targeting U.S. forces in Iraq.

A U.S. official said Tuesday that the Pentagon is investigating whether Iran was behind a January 20 attack in Karbala that left five U.S. troops dead.

“We believe it’s possible the executors of the attack were Iranian or Iranian-trained,” the U.S. official said.

The sophistication of the attack, in which English’speaking guerrillas in American’style uniforms drove sport utility vehicles past checkpoints to attack a government compound, was beyond what insurgents in Iraq have shown they are capable of, U.S. officials said.

Whether Iran proves to be responsible for that attack or not, al-Maliki said his country cannot be a proxy battleground for Washington and Tehran.

“Iraq has nothing to do with the American-Iranian struggle, and we will not let Iran play a role against the American Army and we will not allow America to play a role against the Iranian army, and everyone should respect the sovereignty of Iraq,” al-Maliki said.

“We will not accept Iran to use Iraq to attack the American forces.”

Iran was a major topic Wednesday during CNN correspondent Michael Ware’s wide-ranging, exclusive interview with al-Maliki.