Fifteen diplomatic posts in high-threat areas fail to meet safety standards 10 months after the attacks that killed four Americans, including the U.S. ambassador, in Benghazi, Libya, State Department officials told Congress on Tuesday.

Gregory Starr, the State Department’s director of diplomatic service, told the Senate Foreign Relations Committee that modifying many of those buildings in their current locations is not possible. He said some of the buildings are not far enough from the street or other public areas to be adequately protected.

“We cannot retrofit many of our buildings to withstand blasts or direct attacks without the ability to move to a new location … and build a new facility,” he said.

Sen. Bob Corker, R-Tenn., said he thought the State Department should be more careful about how it chose to spend the $2.2 billion it’s requested for embassy security. “A lot of money (is) being spent in places that, candidly, the security issues are not necessarily urgent,” he said, citing Oslo, Norway, and The Hague in the Netherlands as examples. Starr countered that global security trends are hard to predict and the department must address short- and long-term needs.

Starr also said that State Department plans to hire 151 new security agents over the next two years to bolster diplomatic security.

Current concerns about diplomatic security date to the Sept. 11, 2012, attacks on U.S. outposts in Benghazi. Ambassador Christopher Stevens and State Department computer expert Sean Smith died of smoke inhalation when the building they were in was set on fire, and CIA security contractors Glen Doherty and Tyrone Woods were killed hours later when armed militants attacked a CIA annex nearby. A State Department internal investigation found that security at the Benghazi mission was “grossly inadequate” and filled with “relatively inexperienced” officers.

Four State Department officials are still on administrative leave awaiting further action after the review. Corker said he was concerned that the inaction has led to “a lack of accountability” and that personnel issues are an important piece of the puzzle.

“Too often security issues seem to come down to more money when they are more the result of a failure to prioritize resources or a lack of leadership to respond appropriately when threats emerge,” Corker said in a statement released after the hearing.

Starr is now the State Department’s top official on diplomatic security. The assistant secretary for diplomatic security position is still vacant after the December resignation of Eric Boswell after the accountability results were released.

While Starr told senators that Secretary of State John Kerry was reviewing those on administrative leave, as well as the circumstances of the attack, he went on to praise the reprimanded officers.

“These are people that have given their careers to diplomatic security as well and the security of the Department of State, and I have a great deal of admiration for them,” Starr said. “It does not excuse the fact that we had a terrible tragedy in Benghazi … (but) all through the years that we’ve had multiple attacks in Yemen and in Afghanistan and in Iraq, those people performed admirably.”

The hearing’s main intent was to discuss an embassy security bill sponsored by committee chairman Sen. Robert Menendez, D-N.J. The bill would authorize money for embassy security, Arabic language training and a Foreign Affairs Security Training Center, while also directing the State Department to prioritize safety over cost when awarding contracts.

“We must strike the proper balance between sealing off vulnerabilities in high-threat areas and continuing to conduct vigorous and effective diplomacy that serves the national interest,” Menendez said.