U.S. Defense Secretary Leon Panetta says the United States has no choice but to maintain good relations with Pakistan, despite its alleged links to various militant groups.

During a public forum with Secretary of State Hillary Clinton in Washington Tuesday, Panetta said Pakistan has ties to the Haqqani network in the country's northwest that conducts cross-border attacks on U.S. forces in Afghanistan, as well as with Lashkar-e-Taiba militants who attacked India.

Both groups are listed by the United States as terrorist organizations.

Panetta said Washington's ties with Islamabad remain essential also because America is fighting al-Qaida there, because Pakistan represents an important force in the region, and because the country has nuclear weapons and Washington is concerned about what would happen to those weapons.

Clinton said the Obama administration considers relations with Pakistan to be of “paramount importance.” She said that although there have been numerous “challenges” in bilateral ties over the years, she credits Islamabad with lately recognizing its shared interest with Washington in confronting terrorism.

Earlier in the day, the U.S. State Department and the U.N. sanctions committee designated key Haqqani network commander Sangeen Zadran a terrorist, freezing any U.S. assets he has and barring Americans from doing business with him. In addition, the U.N. decision subjects him to a global travel ban, an asset freeze and an arms embargo.

U.S. officials say Zadran is the shadow governor of Afghanistan's eastern Paktika province, and has been connected with many roadside bombings and kidnappings of Afghans and foreign nationals in the border region between Afghanistan and Pakistan.