Congress has been investigating what was believed to be the collapse of the U.S. intelligence network in Iran and Lebanon.

Officials said the intelligence committees in the House and Senate have been briefed on the arrest of at least a dozen CIA operatives in Lebanon. They said the arrests badly damaged U.S. monitoring of Iran and its chief proxy, Hizbullah.

“It is hard to overestimate the damage,” an official said.

In October 2011, House Intelligence Committee chairman Rep. Mike Rogers flew to Beirut to interview CIA officers. Officials said the visit by Rogers was meant to determine CIA responsibility for the Hizbullah arrest of key operatives in Iran and Lebanon. Hizbullah members have been appointed to 16 of the 30 ministries in the Lebanese government.

Officials said Hizbullah, believed to have tracked cellular phone records, exploited CIA mistakes to track and identify U.S. operatives in Lebanon. They said the paid Lebanese informants, including Hizbullah members, formed two espionage cells eventually exposed by double agents.

In June 2011, Hizbullah secretary-general Hassan Nasrallah announced the arrest of three suspected CIA informants.

“We were lazy and the CIA is now flying blind against Hizbullah,” a former official told ABC News.

The CIA network in Iran was also believed to have been dismantled in May 2011. Congress was said to have been investigating reports that Iranian intelligence discovered CIA communications that relayed orders to as many as 30 operatives.

The House committee was also examining information that the CIA was warned that its network in Lebanon was likely to have been infiltrated by Hizbullah. Officials said Rogers interviewed the CIA chief in Beirut for details.

Between 2007 and 2009, Hizbullah and the Lebanese government reported the arrest of more than 100 Israeli intelligence agents. Many of the Mossad operatives were said to have planted devices in communications networks of Hizbullah and the Lebanese military.

Officials said the CIA monitored the arrest of the Mossad agents but failed to impose sufficient counter-measures. They said the House and Senate intelligence committees could recommend the dismissal of those in the CIA responsible for the Lebanese network.