International Atomic Energy Agency (IAEA) Director General Mohamed ElBaradei leaves Mehrabad International airport after speaking with journalists in Tehran, Iran yesterday. -Xinhua

Director General of the International Atomic Energy Agency (IAEA) Mohamed ElBaladei arrived in Tehran Thursday morning amid an escalating crisis over the Iranian nuclear issue.

ElBaradei paid the visit upon an invitation extended by chief of Iran's Atomic Energy Organization Gholam-Reza Aqazadeh, the official IRNA news agency reported.

During his visit at a crucial juncture over Iran's nuclear issue, the IAEA chief is scheduled to meet with senior Iranian officials and hold consultations with them on the continuation of Iran's constructive interaction and cooperation with the UN nuclear watchdog, the report added.

Upon his arrival at the Tehran airport, ElBaradei stressed the importance to solve the Iranian nuclear issue through political means and negotiations, urging the Islamic Republic to re-suspend all activities related to uranium enrichment according to a presidential statement of the UN Security Council.

"My trip is aimed to clarify remaining prominent issues over the Iranian nuclear issue, and I hope that I can persuade Iran to adopt confidence-building measures such as re-suspension of uranium enrichment activities," he told reporters.

ElBaradei's visit came just two days after Iran announced that it had successfully produced low-grade enriched uranium and come at the threshold of global nuclear club.

On Tuesday, Iranian President Mohammad Ahmadinejad and Aqazadeh, who is also deputy president, officially declared that Iran has gained ticket to join global nuclear club by having produced 3.5 percent enriched uranium on Sunday, a technological leap in the process for nuclear power plant construction.

Aqazadeh also said that the achievement means that Iran has "passed the stage of pilot production" and has paved the way for launching 3,000 centrifuges by the end of the current Iranian calendar year, which ended on March 20, 2007.

On Wednesday, Aqazadeh's deputy Mohammad Saeedi said that Iran had informed the IAEA of the decision to upgrade Iran's uranium enrichment to a degree of 3,000 centrifuges.

Iran's announcement of nuclear achievement has been believed to make the ongoing ElBaradei trip uncertain, which had been viewed as a last-ditch effort to ease the rising Iranian nuclear crisis.

Former Iranian President and the incumbent Expediency Council Chairman Akbar Hashemi Rafsanjani said on Tuesday that the situation of the Iranian nuclear issue had become "very complicated" and ElBaradei would "encounter a new situation once he enters Iran."

The UN Security Council, in a presidential statement adopted on March 29, granted Iran 30 days to comply, but the requirement has been rejected by Tehran as illegal.