NEW DELHI: Just two days after a drone strike killed al-Qaida's second-in-command, Defense Secretary Leon Panetta made it clear Wednesday that such attacks will continue as long as the US needs to defend itself against terrorists that threaten America.

Speaking in India, Panetta unapologetically dismissed suggestions that the strikes could violate Pakistan's sovereignty.

''This is about our sovereignty as well,'' he said when answering questions from the audience after a speech at an Indian think tank. And he was blunt about the difficulties in the US relationship with Pakistan, as insurgents continue to find safe haven there, despite repeated protests from American leaders.

''It's a complicated relationship, often times frustrating, often times difficult,'' Panetta said. ''They have provided some cooperation. There are other times when frankly that cooperation is not there. But the United States cannot just walk away from that relationship. We have to continue to do what we can to try to improve (the) areas where we can find some mutual cooperation.''

Panetta's message is likely to reverberate in Pakistan, particularly since it was delivered in India.

But he also publically urged India to work toward a better relationship with Pakistan, its fellow nuclear-armed neighbor.

Both the US and India must overcome deep differences with Pakistan to bolster peace and security in South Asia, he said in a speech to the Institute for Defense Studies and Analyses here.

''Pakistan is a complicated relationship, complicated for both of our countries but it is one that we must continue to work to improve,'' Panetta said. ''India and the United States will need to continue to engage Pakistan, overcoming our respective — and often deep — differences with Pakistan to make all of South Asia peaceful and prosperous.''

He said he welcomed steps that India and Pakistan have taken to normalize trade relations as key to resolving their differences and a way to help Pakistan counter extremism within its borders.

But Panetta's speech comes as US tensions with Pakistan continue to fray, strained by the persistent CIA drone attacks that target insurgents inside Pakistan as well as a deadlock in negotiation over US shipments of supplies across the Afghanistan border.

Adding to that potential discord, Panetta also urged Indian leaders in meetings Tuesday and Wednesday to consider providing additional support to Afghanistan, including trade, reconstruction and assistance for the Afghan security forces.