"This is a legal matter which cannot be influenced by any political decision," the minister told Aljazeera.
In Washington, where he was meeting Bulgarian President Georgi Parvanov, Bush had said: "The nurses ought to be freed.
"There should be no confusion in the Libyan government's mind that those nurses ought to be, not only spared their life, but out of prison.
"We will continue to make that message perfectly clear."
The five nurses and a Palestinian doctor are under death sentence in a Libyan jail and could face a firing squad. They were convicted last year, after six-and-a-half years in jail, of infecting children with the HIV virus at a hospital in Benghazi, in northern Libya.
Of the 380 children that were infected, 47 have died.
Two nurses and the doctor initially confessed to the charges but later claimed police extracted their confessions with torture including beatings and electric shocks.