WASHINGTON: US President Barack Obama has signed into law a bill designed to bar Iran’s future ambassador to the United Nations.

“I have signed into law an act concerning visa limitations for certain representatives to the United Nations,” President Obama said in a statement issued by his office on Friday evening.

The new law says that “no individual may be admitted to the United States as a representative to the United Nations, if that individual has been found to have been engaged in espionage or terrorist activity directed against the United States or its allies, and if that individual may pose a threat to US national security interests.”

The United States claims that Iran’s new ambassador for the United Nations, Hamid Aboutalebi, participated in the 1979 Iran hostage crisis at the American Embassy in Tehran.

The dispute threatens to derail a cautious thaw in relations between the United States and Iran over Tehran’s nuclear programme.

President Obama, however, indicated that the new law cannot prevent him from seeking to engage Iran for a peaceful resolution of the nuclear dispute.

He said he would only regard the legislation as guidance and will not allow it to infringe upon his executive powers.

The Obama administration had made it clear last week that it would not issue a visa to Mr Aboutalebi because he was involved in the hostage crisis in Tehran.

His selection also angered the US Congress as lawmakers pledged to block him from coming to the UN headquarters in New York to take charge of his office.

Although President Obama signed the bill into law, he cited precedent established by former President George H. W. Bush, who refused to accept the laws that limited his executive power.

The new law, Mr Obama warned, could restrict his powers to accept or reject the credentials of foreign ambassadors and said that he would treat the new law as an “advisory” only.

“Acts of espionage and terrorism against the United States and our allies are unquestionably problems of the utmost gravity,” he said.

“I share Congress’s concern that individuals who have engaged in such activity may use the cover of diplomacy to gain access to our nation.”

Mr Aboutalebi’s selection also alarmed the US media, which claimed that he played a significant role in the 1979 militant takeover of the US Embassy in Tehran, when dozens of American diplomats and staff were held for 444 days as hostages.

The protracted standoff led to the severing of all diplomatic ties between the US and Iran for the past three decades.

As the host government, the United States is generally obliged to issue visas to diplomats who serve at the United Nations but it is refusing to do so for Mr Aboutalebi.

Iran, however, has rejected the US protest, saying that Mr Aboutalebi is a veteran diplomat who heads Iranian President Hassan Rouhani’s political affairs bureau. Tehran also says that Mr Aboutalebi did not participate in the hostage-taking in November 1979, when a Muslim student group seized the US Embassy after the overthrow of the Shah.

Mr Aboutalebi, however, has acknowledged he served a limited role as a translator for the students who took the Americans hostage.