The new legislation bars from entering US soil "any representative to United Nations who the President determines has been engaged in terrorist activity against the US or its allies and may pose a threat to America’s national security interests."
Obama said as the former US president George Bush observed in signing the Foreign Relations Authorisation Act, Fiscal Years 1990 and 1991, this provision "could constrain the exercise of my exclusive constitutional authority to receive within United States certain foreign ambassadors to United Nations."
"Acts of espionage and terrorism against United States and our allies are unquestionably problems of the utmost gravity, and I share the Congress's concern that individuals who have engaged in such activity may use the cover of diplomacy to gain access to our nation," he said in a statement on Friday.
Nevertheless, as president Bush also observed, "curtailing by statute my constitutional discretion to receive or reject ambassadors is neither a permissible nor a practical solution."
So the measure should be taken as an "advisory," because it could potentially interfere with his "constitutional discretion" to receive or reject ambassadors, he said.
The decision of the United States to deny a visa to the Iran's nominee to United Nations could have wide international ramifications. Aboutalebi is a top adviser to Iranian president Hassan Rouhani.
The White House Press Secretary Jay Carney said, since Iranian election, the US has been pursuing with Iran a very a clear-eyed effort with its allies on the P5-plus-1 to press Iran to forsake and give up its nuclear weapons programme.
"We continue to work on that effort," Carney added.

In 1979, dozens of American diplomats and staff were held for 444 days by radical Iranian students at the US embassy in Tehran after the overthrow of the pro-Western shah.
The standoff led to the severing of all diplomatic ties between the US and Iran for the past three decades. Aboutalebi has insisted he was not part of the hostage-taking in November 1979.


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