The US Senate has voted to block a $23m payment to Uzbekistan, after the Uzbek government ended an agreement for US troops to use an airbase there.
The Uzbek base has been a key hub for US troops
The payment, for past use of the base, will be postponed for at least a year.
The Karshi-Khanabad base has been an integral part of US military operations in the region for nearly four years.
But in July, Tashkent asked the US to leave the base, after it criticised the violent suppression of demonstrations in the town of Andijan in May.
"Paying our bills is important. But more important is America's standing up for itself, avoiding the mis-impression that we overlook massacres and avoiding cash transfers to the treasury of a dictator," said Republican Senator John McCain, who sponsored the amendment that will block payment.
Mr McCain said the actions of Uzbek President Islam Karimov were so alarming that the Senate should be considering sanctions against him, "not how to transfer millions of taxpayers' dollars to his government."
The airbase at Karshi-Khanabad (K-2), in south-eastern Uzbekistan, has been an important hub for US operations in neighbouring Afghanistan following the 11 September 2001 attacks.
Its location in a secure area, a short journey from the Afghan border, made it an ideal logistical centre.
But in July the Uzbek government gave American troops six months to leave the base - a move which analysts say is linked to American criticism over the bloody suppression of unrest in Andijan.
There are still disputed versions of exactly what happened in the incident, when troops fired on a crowd of people.
The government says the violence was the result of an attempt by Islamic militants to seize power, and puts the number of dead at 187.
But witnesses say more than 500 people were killed, and human rights groups have repeatedly called for an international investigation.