The United States on Tuesday condemned a vote by Rwandan lawmakers to approve a change to their constitution to allow President Paul Kagame to serve a third term.
A State Department spokesman did not explicitly threaten that US aid to its traditionally close African friend would be cut, but warned ties could be reviewed.
The Rwandan senate's decision to approve an amendment to the constitution must still go to a referendum, but is seen as likely to pass with little opposition.
"The United States notes with great concern the Rwandan senate's vote today," State Department deputy spokesman Mark Toner told reporters in Washington.
"We expect President Kagame to follow through on the commitments he has made previously to foster a new generation of leaders in Rwanda and to step down at the end of his current term in 2017," he warned.
Asked whether the United States would consider reducing the assistance it provides to Rwanda if Kagame remains in office beyond the end of his term, Toner was cautious.
"If he decides to remain in office, then that could impact US-Rwanda relations going forward," he said.
Kagame has run Rwanda since his ethnic Tutsi rebel army ended the 1994 genocide and ousted Hutu extremists.
He won elections in 2003 and 2010 and -- under the current constitution -- is bound to step aside in 2017 at the end of his second term.
If passed, the new law would allow him to run for one more seven year term and then two more of five years, potentially keeping him in office until 2034.
Washington has usually maintained good relations with a leader it sees as having brought stability and a measure of prosperity to a country blighted by genocide.
But it opposes indefinite presidential terms for African leaders, arguing that this harms efforts to build accountable democratic institutions.
And, while Kagame apparently retains broad public support, his critics have accused him of displaying increasingly authoritarian tendencies.