US Senator Lindsey Graham (C) speaks during a press conference while US Senator John McCain (L) looks on at the US Embassy in Kabul on January 2, 2014.
A decision to release jailed Taliban militants further aggravated US-Afghan relations on Thursday as pressure mounts for the two countries to sign a deal allowing some American soldiers to stay after 2014.
The plan to free 88 insurgent suspects from Bagram jail has outraged US military officials and senators as final negotiations are underway on the long-delayed Bilateral Security Agreement (BSA).
Republican Senator Lindsey Graham, an influential voice on US military issues, tore into the proposed release of militants who he said had "blood on their hands".
"If this release goes forward, it... would have an unbelievably negative impact on the future relationship between the American people and the Afghan government," Graham said on a visit to Kabul.
Graham, who spoke at the American embassy alongside former US presidential nominee John McCain, said freeing the prisoners would do "irreparable damage" to US-Afghan ties.
"The 88, to me, represent a defining moment in our relationship," Graham said, adding that the jailed men were responsible for over 60 NATO coalition and 57 Afghan deaths.
After a meeting with President Hamid Karzai, Senator McCain said he expected the BSA to be signed soon, despite months of public wrangling and the threat of a complete pullout by US-led NATO forces.
"I am confident from our conversation that the differences have been narrowed to a point where we could get things resolved in a very short time," he said.
"We don't want to see a repeat of what happened in Iraq where we won the war but lost the peace because of a complete withdrawal."
McCain said the proposed prisoner releases did "damage, so we will have to see exactly what transpires before reaching a conclusion as to what actions could be taken".
Bagram jail was finally handed over to Afghan control by the US in March after another public stand-off with Karzai, who has depicted the jail as a symbol of Afghanistan's efforts to regain its national sovereignty.
Many of those still held in Bagram are suspected high-level Taliban fighters, and the US has long been concerned Afghanistan's weak and corruption-prone security forces could allow them to return to the battlefield.