Five visiting U.S. senators took a hard line with Afghan President Hamid Karzai on Sunday, outlining issues that could endanger a long-term partnership between the two nations and emphasizing the importance of American-led night raids as U.S. forces withdraw from the conflict.

Sen. John McCain (R-Ariz.) said he was encouraged by “significant military advances on the ground” but was unsympathetic to Karzai’s demand that the United States curb its night operations, which the Afghan leader says result in dozens of civilian casualties each year. Sen. Lindsey O. Graham (R-S.C.), another member of the delegation, said that handing over detention operations to Afghans — another key Karzai demand — would “put American lives in danger.”

U.S. officials have struggled for more than a year to craft a partnership agreement that would include a role for American troops and diplomats beyond 2014, when NATO forces are scheduled to leave Afghanistan. Karzai has said repeatedly that without an end to the night raids and a handover of U.S.-run detention facilities, he will not sign such an agreement.

McCain emphasized the importance of finalizing an agreement before a NATO summit in May, when the alliance is due to discuss the future of its involvement in Afghanistan.

“Absent that, I could see the possibility of real fissures developing amongst the alliance,” McCain said.

Graham said he would like the U.S. military to maintain a footprint in Afghanistan beyond 2014 “that would allow us to have a couple of bases with Special Forces units that would always provide the edge to the Afghan security forces against future insurgent attacks.”

Members of the delegation, which included Sens. John Hoeven (R-N.D.), Jeff Sessions (R-Ala.) and Richard Blumenthal (D-Conn.), met with Karzai and Gen. John R. Allen, the top U.S. commander in Afghanistan, as well as members of the country’s opposition parties.

McCain voiced doubts about the viability of a political settlement with the Taliban, saying that President Obama’s announcement of a military drawdown has diminished the insurgents’ willingness to negotiate.

“When they think you’re leaving, obviously they’re not going to be serious about negotiations,” the senator said.

McCain also said that he opposes the release of five Taliban prisoners as part of the negotiations, a concession that U.S. officials had discussed in early peace talks. A decision to release the men, being held at the Guantanamo Bay military prison, would have to be approved by Congress.