A new U.S. strategy to break a stalemate in Afghanistan will require additional American troops, the head of the U.S. Central Command said on Thursday.

"I do believe it will involve additional forces to ensure that we can make the advice and assist mission more effective," Army General Joseph Votel said during a Senate Armed Services Committee hearing.

Votel said a strategy was still being developed and did not give details on the number of troops that would be required or when a final decision would be made.

Last month, Army General John Nicholson, the top U.S. commander in Afghanistan, said he needed several thousand more international troops in order to break the stalemate in the long war with Taliban insurgents, signaling that the matter may soon be put before President Donald Trump.

So far, Trump has offered little clarity about whether he might approve more forces for Afghanistan, where some 8,400 U.S. troops remain more than 15 years after the Islamist Taliban government was toppled by U.S.-backed Afghan forces.

The difficult situation in Afghanistan was highlighted on Wednesday when 49 people were killed following an attack on a military hospital in Kabul by gunmen.

The gunmen went through the 400-bed hospital, shooting doctors, patients and visitors and battling security forces for several hours in a sophisticated operation. Daesh claimed responsibility for the attack.

The requests for additional troop deployment and the latest terrorist attack come as the U.S. State Department said on Thursday it will soon run out of visas for interpreters and other Afghans who have worked for the U.S. government during the war.

At least one Senator, Democrat Jeanne Shaheen, said any decision to let the program lapse sends a message to allies in Afghanistan that the US is not supporting them. She pledged to immediately introduce legislation to provide more visas. "It's both a moral and practical imperative that Congress right this wrong immediately," Shaheen said in a statement. Her office said more than 10,000 applicants are still in the process of obtaining visas.

Shaheen and Republican Senator John McCain led a failed effort last year to pass legislation extending to 4,000 more people an existing special immigrant visa program for Afghans who assisted U.S. forces.

The National Defense Authorization Act passed late last year added 1,500 visas to the program, while tightening requirements for eligibility.

Meanwhile officials prepare to implement the President's executive order signed this week that temporarily bans the admission of refugees and some travelers from six countries. Afghanistan is not one of them. The new order is set to take effect on the 16th of March.