Fearful that US failure there could unleash the Taliban and other Islamist insurgencies, Russia may help NATO open a supply line through former Soviet territory.
Though largely symbolic, the law could be having lasting implications.
The special representative launched his three-day visit in Pakistan Tuesday with an aim to 'listen and learn,' but also to urge the US ally to eliminate its militant havens.
Biden opens a door on Iran, but presses allies on Afghanistan.
But Pentagon officials say Kyrgyzstan's move to close a supply route won't impede operations in Afghanistan.
US State Department officials said the US could offer to pay the Kyrgyz government more for the base.