Pakistan's spy agency ISI not only supports but also encourages terrorist outfits, particularly the Haqqani militant network, the US said on Friday, underlining that it expected the Pakistani leadership to snap these ties.

"All I can tell you that we are confident that the ISI continues to support and even encourage the Haqqanis to launch these attacks. I am not going into specifics of the intelligence that we have about the support," Captain John Kirby, spokesperson of Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, told Pentagon reporters during an off-camera interaction.

When asked about the denial being issued by the Pakistani leadership on the allegations, Kirby said that he and the chairman stand by those comments.

"The chairman stands by what he testified before the US Senate," he said. Mullen told lawmakers yesterday that the Haqqani network, "acts as a veritable arm of Pakistan's internal services intelligence agency."

"With ISI support, the Haqqani operatives planned and conducted that truck bomb attack, as well as the assault on our embassy. We also have credible intelligence that they were behind the June 28th attack on the Intercontinental Hotel in Kabul and a host of other smaller, but effective operations,'' Mullen said on the Capitol Hill.

Kirby said the the chairman made it very clear on Thursday. "He used Haqqani as an example. If you look at his statements that there are other extremist groups such as the Queta Shoura that has the ISI support,'' the spokesperson of Mullen said.

When asked if the US is considering the option of declaring ISI itself as a terrorist outfit now that it has the evidence of its links, Kirby responded: "I am not going to go further than what he (Mullen) said".

Kirby said Mullen did not make any characterization but indicated that the US aid to Pakistan would be conditioned in its support and progress made in the war against terrorism.

He said aid assistance to Pakistan will be based on the the level to which "Pakistani government is to assist in the war against terrorism".

He made it clear that while Mullen wants to pursue his relationship with the Pakistani military and the ISI by extension, there was the for Pakistan to do more as partners in this fight.

"They know and we made it clear that aid and assistance is depended upon the degree to which those efforts continue,'' Kirby said, but added that he was not aware of any deadline in this regard.

The spokesperson of Mullen said the US was assessing the aid assistance to Pakistan. When asked whether the US military aid directly or indirectly supported the attack on the US Embassy in Kabul, he said it was for the ISI to answer.

"We believe that they (ISI) are supporting indirectly and directly (to the Haqqani network). That is as far as I can go at this point of time," he said. He said the US administration has made it "very very clear the sense of urgency" over the issue and the Pakistani leadership is "very aware of our concerns".

Mullen, he said has met the Pakistan Army Chief General Ashfaq Parvez Kayani at least 30 times to improve relationships with Pakistan. "When he has felt strongly enough that the partnership that we were trying to build with Pakistan was not conducive to those ends, he made it clear -- both publicly and privately to General Kayani," Mullen's spokesperson said.

He said the decision to "speak publicly" on the issue has been a deliberate decision "because he felt that strongly about the issue". Kirby said there has been a long standing historical relationship between the ISI and the extremist groups. "There has been a lot of activity over the course of this summer -- the hotel attack in Kabul, Wardak truck bomb, attack on the Embassy and others smaller level operations," he noted, adding "It has gone worse."

The activities of the Haqqani network "have become more brazen, more aggressive and more lethal," he said, adding "information has become more available that these attacks have been supported or encouraged by the ISI."

Kirby said Mullen, who held talks with General Kayani last week in Spain, decided to 'speak publicly' on the issue because 'this is the truth'.