The Obama administration intensified its objections on Tuesday to Iran’s nomination for United Nations ambassador, a former translator whose role in the 1979-81 Tehran hostage crisis has touched American political nerves, asserting that the choice was “not viable” in what seemed as close as possible to ruling it out.

The assertion, made by the White House press secretary, Jay Carney, came hours after the Senate voted unanimously on Monday night on a bipartisan measure that would bar the nominee, Hamid Aboutalebi, from taking the United Nations post by denying him a visa. House passage of the measure was considered a near certainty.

The administration’s objections over the nominee could turn into a new confrontation with the Iranian government at precisely the time when it is seeking to improve the diplomatic climate for talks on Iran’s disputed nuclear program, which resumed on Tuesday in Vienna.

While the United States is obliged to grant visas to United Nations diplomats from all countries, even those it finds objectionable, it has reserved the right to disallow anyone known to have played a role in the Iranian student revolutionary movement that seized the American Embassy in Tehran in 1979, holding American hostages for 444 days. The hostage crisis was the defining event that to this day has helped shape the estranged relations between Iran and the United States.