While Pakistan's Inter-Service Intelligence agency refuses to admit it backs the radical, al Qaeda-linked Lashkar-e-Taiba, US intelligence officials and even Lashkar-e-Taiba operatives beg to differ. From a report in The New York Times on Lashkar-e-Taiba and its attack on Mumbai, India:

But a senior American intelligence official said the ISI was believed to maintain ties with Lashkar. Four Lashkar members, interviewed individually, said only a thin distance separated Lashkar and the ISI, bridged by former ISI and military officials.

One highly placed Lashkar militant said the Mumbai attackers were part of groups trained by former Pakistani military and intelligence officials at Lashkar camps. Others had direct knowledge that retired army and ISI officials trained Lashkar recruits as late as last year.

“Some people of the ISI knew about the plan and closed their eyes,” said one senior Lashkar operative in Karachi who said he had met some of the gunmen before they left for the Mumbai assault, though he did not know what their mission would be.

Former ISI officials, such as retired Lieutenant General Hamid Gul, the intelligence service's former director, openly support groups such as Lashkar-e-Taiba, the Taliban, and al Qaeda, yet they are untouchable in Pakistan.

For more on the ISI's links to terror groups, see "Pakistan's Jihad," written by Tom Joscelyn and me in December last year.