The Obama administration said on Wednesday that Iran’s nomination of a former hostage-taker as its ambassador to the United Nations is “extremely troubling”, the BBC reported.

State Department spokeswoman Marie Harf said at Wednesday’s daily briefing, “I will say that we think this nomination would be extremely troubling.”

She added, “We’re taking a close look at the case now, and we’ve raised our serious concerns about this possible nomination with the government of Iran.”

Earlier this week ,the Iranian government applied for a U.S. visa for Hamid Aboutalebi, Iran’s former ambassador to Belgium and Italy, who was a member of the Muslim Students Following the Imam’s Line, a group of radical students that seized the U.S. embassy on November 4, 1979, and held its staff hostage for 444 days.

Aboutalebi has reportedly said he had minimal involvement in the hostage-taking group, according to the BBC.

Senators have also balked at Iran’s pick of Aboutalebi, and Senator Ted Cruz said he will introduce legislation to block Iran’s application for a visa for him.

“It is unconscionable that in the name of international diplomatic protocol, the United States would be forced to host a foreign national who showed a brutal disregard of the status of diplomats when they were stationed in his country,” Cruz said, according to the BBC.

“This person is an acknowledged terrorist,” he added.

His legislation would require President Barack Obama to deny a visa to any UN applicant determined to have engaged in terrorist activity.

Iranian President Hassan Rouhani reportedly tapped Aboutalebi for the UN position after an interim deal on Iran’s nuclear weapons program was reached in Geneva last November.

Rouhani has tried to present himself to the West as a “moderate”, a fact which allowed the signing of the interim deal. At the same time he has been criticized by the UN over his failure to fulfill his campaign promises to allow greater freedom of expression.

Shortly after Rouhani was elected, reports indicated that he had an alleged link to terrorism. The Argentine government prosecutor said that Rouhani was on the special Iranian government committee that plotted the 1994 bombing of a Jewish community center in Buenos Aires.