“As we’ve seen in recent weeks with attacks against our embassies in Egypt, Libya and Yemen, our diplomatic personnel are at the mercy of daily threats in hostile regions of the world, and their safety and security must be our top priority,” Portman said in a statement Wednesday.

In a letter sent Wednesday to Defense Secretary Leon Panetta, McCain and Portman said they know it is primarily the State Department’s job to protect U.S. missions overseas, but said Defense should also look into what it could have done to prevent the deaths that occurred in Libya on Sept. 11, 2012.

“While the State Department is ultimately responsible for ensuring their protection, it's vital that we conduct thorough oversight of the Defense Department, which plays an important role in supporting the protection of our U.S. missions overseas,” Portman said.

There have also been outbreaks of violence at U.S. embassies in Egypt and Yemen. The two senators said the State Department had already been asked to review those incidents and said the Defense Department should do the same.

“As investigations by the Justice Department and the State Department into the attacks in Benghazi progress, we feel it is appropriate and necessary that the Defense Department thoroughly reviews the support it provided to the U.S. mission in Libya and takes the necessary steps to ensure improvements are made where necessary to best support diplomatic security worldwide,” the letter stated.

Earlier Wednesday, the House Oversight and Government Reform Committee held the first hearing on the Libyan attack, where one witness said more security wouldn’t have prevented the deaths of Americans in Libya.