ISLAMABAD (Reuters) — U.S. Senator John McCain said on Sunday there could be “no peace” in Afghanistan or the rest of the region without Pakistan’s cooperation, as he visited Islamabad ahead of a review from the United States of its Afghan war strategy. McCain, chairman of the Senate Armed Services Committee, met Sartaj Aziz, Pakistan’s top foreign policy official, and also met army chief General Qamar Javed Bajwa.

U.S. officials say they seek greater cooperation with Pakistan, not a rupture in ties, after the review the 16-year-old war in Afghanistan, due in mid-July, where some 8,800 U.S. troops remain to support the Western-backed government.

U.S. President Donald Trump’s administration is exploring hardening its approach toward Islamabad over Pakistan-based militants launching attacks in Afghanistan, two U.S. officials told Reuters last month. “We will not have peace in the region without Pakistan,” McCain, who was accompanied by senators Lindsey Graham, Elizabeth Warren, Sheldon Whitehouse and David Perdue, said later.

Experts on America’s longest war say militant safe havens in Pakistan have allowed Taliban-linked insurgents a place to plot attacks in Afghanistan and regroup after ground offensives. Critics say Islamabad is not doing enough to crack down on militants such as the Taliban-affiliated Haqqani network.

Pakistan argues that it has done a great deal to help the U.S. in tracking down terrorists and points out that it has suffered hundreds of deaths in Islamist militants attacks in response to its crackdowns.

Pakistan last week also reacted sharply when the U.S. State Department on June 26 designated as a terrorist Syed Salahuddin, leader of the largest Kashmiri militant group fighting against Indian rule, accusing the U.S. of acquiescing to the wishes of visiting Indian Prime Minister Narendra Modi. Kashmir, ruled in part by India and Pakistan and claimed in entirety by both, is a hot-button issue between the nuclear-armed neighbors, which have fought two of their three wars since independence from Britain over the territory.