Special US Representative for Afghanistan and Pakistan Richard Holbrooke told the Pakistani leaders to prove that they were "serious" in the fight against terrorism, when he met them on the sidelines of a meeting on Afghanistan at Hague.

"I think there's almost no issue (commitment of Pakistan in taking action against terrorism) that's been as hotly debated as that one, and I have heard conflicting views," Holbrooke told the National Public Radio on Tuesday.

"This morning, Secretary of State Hillary Clinton [Images] and I met with the foreign minister of Pakistan Qureshi, and with the head of Inter-Services Intelligence, General (Ahmed Shuja) Pasha, and we went right to the heart of it," he added.

"General Pasha and Minister Qureshi said, we know that some people don't think we're serious, but we are serious. That's them speaking," Holbrooke said, adding, "And our response was, well, the proof is in the pudding. We need to work together for practical results."

Holbrooke said the attack on policy academy in Lahore [Images] came up prominently during the meeting with the Pak foreign minister and the ISI chief.

"The Foreign Minister said this is an attack on our very essence. It's outrageous. We want to work with you to root this out. So there's a lot of concern, and I think it's growing, in Pakistan as the violence spreads out of the tribal areas and eastward into Swat and now even into Lahore," Holbrooke said.