Iraqi Prime Minister Nouri al-Maliki told a visiting U.S. congressional delegation Friday that it could not visit a camp of Iranian dissidents where 34 people died in clashes with Iraqi security forces in April, the delegation’s head said.

After arriving in Baghdad on Friday morning, the six-member group led by Rep. Dana Rohrabacher (R-Calif.) met with Maliki to discuss reconstruction efforts and conditions at Camp Ashraf. The facility is home to 3,000 Iranians who are part of Mujaheddin-e-Khalq, or MEK, a banned Iranian opposition group.

Rohrabacher said that the delegation had hoped to visit the camp Friday on their way to Kurdistan but that Maliki denied their request, citing Iraq’s sovereignty.

Rohrabacher, a senior member of the House Foreign Affairs Committee, said he will now press for a “criminal” probe of whether Iraq has mistreated the dissidents.

“We are investigating to see if criminal behavior caused the death of these noncombatants,” Rohrabacher said. “The killing of unarmed people . . . a mass killing . . . is a criminal act and a crime against humanity.”

The MEK, which the United States still considers a terrorist organization, was behind a wave of attacks against Iran in the early 1980s, although it renounced violence in 2001. But the international human rights community has become increasingly concerned about conditions inside the group’s sprawling settlement near Iraq’s border with Iran.

After the 2003 invasion of Iraq, the United States pledged to safeguard the dissidents, but Iran has been urging the Iraqi government to expel them. When Iraqi security forces tried to enter the camp in April, activists say, 34 people were killed. Iraqi government officials have accused the dissidents of provoking the confrontation. Western journalists have also been denied access to the camp.

Rohrabacher did not explain why he thinks the U.S. Congress has the authority to looking into potential criminal conduct in Iraq. But Rep. Louie Gohmert (R-Tex.), who also traveled to Iraq on Friday, warned that Iraq’s “democratic form of government cannot succeed where there is no sunlight.”

“The United States assured the people living in Ashraf that they would be safe,” Gohmert said. “One question is: Did someone ask or order the American troops to move away from Camp Ashraf?”