KABUL, Afghanistan — A bipartisan Senate delegation Tuesday called for more U.S. troops and more aggressive American military action in Afghanistan, as well as pressure on neighboring Pakistan, saying the United States needs “a winning strategy” to end the 16-year war here and prevent the spread of terrorism.

“We are united in our concern that the present situation in Afghanistan is not on a course for success. We need to change that quickly,” Sen. John McCain, R-Arizona, chairman of the Senate Armed Services Committee, said in a news conference at NATO and U.S. military headquarters in the Afghan capital at the end of a three-day visit to the region.

“America is the strongest nation on earth,” but “we are not winning, and obviously we need a new strategy to win,” McCain said. “We are frustrated that this strategy has not been articulated yet.”

The Trump administration has been working for several months on a new policy for the war-torn region, where U.S. and Afghan forces have been fighting insurgents for the past 16 years. But the plans have been delayed by internal debates, while both Afghanistan and Pakistan have faced a renewed rash of suicide bombings and insurgent attacks.

Both McCain and Sen. Lindsey Graham, R-South Carolina, who visited Pakistan and Afghanistan this week with Sen. Elizabeth Warren, D-Massachusetts, and two other committee members, said they planned to take back a message to President Donald Trump that he needs to adopt a bold military plan for the region but also complement it with a strong and informed diplomatic policy.

“If we leave radical Islam alone, we will not be safe at home,” Graham said. He said he plans to tell the president that “he needs to pull all our troops out” or add even more than the 3,000 to 4,000 troops that U.S. military officials have asked for, to turn the current military “stalemate into a success.”

But Graham also said that “throwing more bombs” is not enough, and that the Trump administration needs to put more effort into understanding and influencing regional leaders. “Rex Tillerson needs to come here quick,” he said, referring to the secretary of state, who has not yet visited the insurgent-plagued region.

Many Afghan and U.S. experts have said that Washington needs to provide more political support to the faltering Afghan government and to the stalled peace process, rather than relying on a mainly military policy.

McCain said the group has been only partly satisfied with its visit to Pakistan, which included a military tour of North Waziristan, the tribal region along the Afghan border where the army drove out Islamist militant groups in 2014 and 2015. They said they questioned Pakistani army officials about continued alleged support for the militant Haqqani network.

“We told them the Haqqanis have a safe zone there, and that is not acceptable,” McCain said. “They said they had taken some measures, but we made it clear we expect them to help and cooperate against the Haqqani group and others.”

Pakistan has repeatedly denied harboring the Haqqanis or other extremist militias, but both Afghan and U.S. officials believe those groups are responsible for a number of deadly attacks in Afghanistan. Pakistan and the United States have a long history of security ties, but Pakistan supported Taliban rulers there until it faced U.S. pressure to abandon them.

Despite the urgent tone of the senators’ remarks, McCain predicted that the conflict in Afghanistan would continue “on a low-burning simmer for a long time to come.” But he reiterated that only an aggressive U.S. effort to bolster Afghan military actions would force the Taliban to negotiate. “That won’t happen unless they feel they are losing,” he said.

Taliban insurgents have maintained a steady pace of attacks on major urban centers, including Kabul, and they now control or influence more than 40 percent of the nation’s territory. The strategy advocated by U.S. military officials here, who hosted the senators’ visit, would add several thousand U.S. troops, along with a similar number from NATO countries. They would focus on building a large Afghan special operations force and beefing up the Afghan air force.

Graham said he was impressed with a newly named group of Afghan military officials, saying they had “cleaned house” and moved to make needed reforms. The Afghan defense forces have been criticized for widespread corruption, poor leadership and high rates of desertion.

“The Afghan people don’t want to go back to the darkness,” he said, referring to the repressive years of Taliban religious rule. “They are looking forward to the light, and they need our help.”

The delegation, which also included Sen. Sheldon Whitehouse, D-Rhode Island, and Sen. David Perdue, R-Georgia, toured U.S. military facilities in Afghanistan on Monday, bestowed promotional medals on seven U.S. service members at a ceremony Tuesday and attended a Fourth of July barbecue with U.S. troops here.