Immigration and Customs Enforcement agents ignored or dropped leads and at times entire cases involving terrorist activities because of disputes with the FBI, says a report by federal officials released Monday.

In examining 10 cases that began at ICE and were taken over by the FBI, the inspectors general of the Homeland Security and the Justice departments found that seven suffered from lack of cooperation until they were taken over by the Joint Terrorism Task Forces, which the FBI controls.

The report cited delays and refusals by the FBI involving investigative actions that needed court approval, which led ICE agents to avoid leads and cases that would have required FBI involvement.

"We were ... extremely troubled that ICE agents would say that their agents declined to undertake a case of potential national security significance for such petty reasons," the inspectors general wrote.

Still, they said, "while the hostility to the FBI's dominance in the field of terrorist financing investigations is palpable, we have no direct evidence that any ICE agent has actually been derelict."

The report, which was dated July 2, was posted online Monday by Sen. Charles Grassley, R-Iowa, a member of the Judiciary Committee. He had asked the inspectors general to examine the effectiveness of an agreement between the Homeland Security and Justice departments aimed at addressing the coordination of terrorist financing investigations.

Using a hypothetical example, the report said, if a case involved two leads — one involving illegal drugs and the other involving terrorism — an agent would pursue the drug lead in order to avoid working with the FBI. In such cases, the agent did not always forward the terrorism lead to the joint task force, the report said.

"It seems obvious that the findings of this report justify concerns about a lack of trust between our two largest federal law enforcement agencies. They need to work together in order to do everything possible to protect Americans in the war on terror," Grassley said in a statement.

Grassley said he initially looked into complaints about friction between ICE and FBI agents after reports from retired ICE agent Joe Webber, who led the Houston field office. Webber said the FBI blocked a request for a wiretap on a person who was communicating with someone the Treasury Department had designated a terrorist, according to the senator.

The inspectors general issued a report on that case last year.