A stable, democratic, prosperous Pakistan is considered vital to U.S. interests. U.S. concerns regarding Pakistan include regional and global terrorism; Afghan stability; democratisation and human rights protection; the ongoing Kashmir problem and Pakistan-India tensions; and economic development. A U.S.-Pakistan relationship marked by periods of both co-operation and discord was transformed by the September 2001 terrorist attacks on the United States and the ensuing enlistment of Pakistan as a key ally in U.S.-led counter-terrorism efforts. Top U.S. officials have praised Pakistan for its ongoing co-operation, although doubts exist about Islamabad's commitment to some core U.S. interests. Pakistan is identified as a base for terrorist groups and their supporters operating in Kashmir, India, and Afghanistan. Pakistan's army has conducted unprecedented and largely ineffectual counter-terrorism operations in the country's western tribal areas, where Al Qaeda operatives and their allies are believed to enjoy "safe haven." U.S. officials increasingly are concerned that the cross-border infiltration of Islamist militants from Pakistan into Afghanistan is a key obstacle to defeating the Taliban insurgency. The United States strongly encourages maintenance of a bilateral cease-fire and continued, substantive dialogue between Pakistan and neighbouring India, which have fought three wars since 1947. A perceived Pakistan-India nuclear arms race has been the focus of U.S. non-proliferation efforts in South Asia. Attention to this issue intensified following nuclear tests by both countries in 1998.