The most senior Democrat on the Senate Foreign Relations Committee said on Monday he would not support President Donald Trump's nominee for secretary of state, Rex Tillerson.
Senator Ben Cardin said he was not persuaded to support Tillerson's nomination even after the former Exxon Mobil chief executive spent an hours-long hearing earlier this month seeking to assure lawmakers that he was fit for the job.
Cardin said Tillerson should have described recent Russian and Syrian military actions in the Middle East as "war crimes" when he was asked about those countries during his conformation hearing.
"The power of the Secretary of State to call out wrong, to name and shame, and to fight each day on behalf of the American people and freedom-seeking people the world over is an enduring symbol," Cardin said in a prepared statement.
Syrian President Bashar al-Assad has relied on Russian help to try to suppress rebel opposition to his rule that sprang up in 2011.
During his Jan. 11 confirmation hearing, Tillerson deplored military action in Syria but stopped short of calling Russian President Vladimir Putin a war criminal.
Despite opposition from Democrats, Tillerson is expected to win confirmation.
Republican Senators John McCain and Lindsey Graham said in a statement on Sunday they would vote to approve Tillerson despite their concerns over his relationship with Putin.
Republican Senator Marco Rubio, who grilled Tillerson during the hearing, has not said yet how he will vote.
The committee is to vote on Tillerson later on Monday. A vote in the full, Republican-controlled Senate is expected shortly afterward.