Ignoring Pakistan's protests, the US on Wednesday said the drone attacks against al Qaeda will continue in that country with which it has "often frustrating" and "desperate" relationship.
"We have made it very clear to Pakistani leaders that we will continue to defend ourselves," Defence Secretary Leon Panetta said during an interaction at the Institute of Defence Studies and Analyses (IDSA) here.
His assertion came a day after Pakistan summoned the US envoy in Islamabad and lodged a protest over continued drone strikes, terming these as "unlawful" and violative of the country's sovereignty.
Pakistan lodged the protest soon after a drone attack killed al-Qaeda's second-in-command Abu Yahya al-Libi along with 15 other militants yesterday in its northwestern tribal region.
Admitting that the US' relationship with Pakistan were "complicated", he said it was "often times frustrating, often times desperate, often times difficult." But, at the same time, he said, "It is a necessary relationship."
In a strong defence of the drone strikes, Panetta said it was a matter of guarding the sovereignty of the US as much as it was about protecting Pakistan.
He noted that more than 3,000 American nationals were killed in the 9/11 attacks in New York and the leadership of these attackers was holed up in Pakistan's tribal regions.
Panetta said Pakistan faced the same kinds of threat as the US from the al Qaeda leaders holed up in the Federally Administrated Tribal Areas (FATA).
The strikes were not just about protecting the US but were protecting Pakistan as well since people in that country were also targets of the insurgents, he said. Panetta said that a drone strike in a Pakistani tribal
areas had targeted "another deputy leader" of the al Qaeda. "We had a strike yesterday that hit another deputy leader," he said referring to the killing of Abu Yahya al-Libi.
Noting that India shared a border with Pakistan, Panetta said it was important that New Delhi continued to try and make progress in dealing with Islamabad. He said he welcomed steps that India and Pakistan have taken to normalise trade relations as key to resolving their differences.
"The same thing is true with the United States. We are fighting a war in FATA, we are fighting a war against terrorism," Panetta said wrapping up his nine-day tour of Asia.
He said Pakistan was also a nuclear power and it was "extremely important" for the US to maintain the relationship with Islamabad.
"They have been cooperative often times in their efforts, they have been engaged, as far as we have done, in going after those who threaten their country," he said.
"They have provided some cooperation, there are times when, frankly, the cooperation is not there, but the US cannot just walk away from that relationship," Panetta said.
He said the US was trying to reopen transit centres and supply routes to Afghanistan from Pakistan.
"We are engaging in negotiations with them to try to see whether we can arrive at an agreement that would re-open those areas," Panetta said.