Baghdad (CNN) -- A Lebanese militant wanted by the United States in connection with the killing of five American soldiers in Iraq was released because of lack of evidence, Iraq's prime minister said Saturday.
Nuri al-Maliki's comments came on the heels of growing outrage among U.S. officials over the release Friday of Ali Mussa Daqduq despite last-minute requests by the White House that he be turned over to stand trial in the United States.
In a written statement, al-Maliki said he could not agree to turn over Daqduq to the United States because the "Iraqi judiciary did not agree" the request was in accordance with Iraq's laws.
With the release of Daqduq, at least one U.S. lawmaker has called for U.S. relations with Iraq to be re-evaluated.
"This is an outrage. Families of those who were killed by this terrorist should also be outraged, and appropriate action should be taken in regards to our relations with the Iraqi government," Sen. John McCain, R-Arizona, told reporters Friday.
Daqduq is accused of participating in the January 2007 kidnapping and killing of the five American soldiers in the Iraqi holy city of Karbala.
After he was captured in Basra in March 2007, according to U.S. intelligence officials, Daqduq pretended to be a deaf-mute.
But officials identified him as a 24-year veteran of Hezbollah who admitted to working with the Quds Force, a branch of Iran's Islamic Revolutionary Guard Corps. U.S. military intelligence contended the Quds Force was using Hezbollah as a surrogate in Iraq.
Daqduq was held by the U.S. military as an "enemy combatant." He was the last detainee to be turned over by the United States before a December 2011 deadline to withdraw.
In May, an Iraqi court cleared Daqduq in connection with the killings.
In the statement released Saturday, the prime minister said the Iraqi court ordered Daqduq's release after it determined there was a lack of evidence.
The United States appealed the ruling and provided additional evidence against Daqduq, which the Iraqi court also ruled was insufficient, al-Maliki said.
Daqduq left Iraq shortly after his release for Lebanon, his lawyer said.
"There is no legal reason for his detention. He should have been released months ago," his attorney, Abdulalmehdi al-Mutairi, told CNN.
The case was widely seen as a test of U.S.-Iraqi relations despite the growing political influence of Iran over Iraq.
U.S. officials were reluctant to hand over Daqduq to the Iraqi judiciary over fears that under pressure from Iran, Iraqi authorities would release him.
The U.S. State Department vehemently objected to Daqduq's release and vowed to continue to try to bring him to justice.
"Let me add that as with other terrorists who we believe have committed crimes against Americans, we are going to continue to pursue all legal means to see that Daqduq sees justice for the crimes of which he is accused," State Department spokeswoman Victoria Nuland said Friday
The State Department has been in contact with the Lebanese government, according to Nuland, and will continue to pursue all "legal means" to bring Daqduq to justice.
CNN's Mohammed Tawfeeq reported from Baghdad; CNN's Chelsea J. Carter reported from Atlanta. CNN's Jennifer Rizzo in Washington contributed to this report.