The United States is warning that Iran has taken “further provocative actions” rather than moving towards compromise and cooperation on its nuclear development activities.

Speaking at a meeting of the agency’s board of governors in Vienna, the chief U.S. envoy to the United Nations International Atomic Energy Agency, Joseph Mcmanus said Iran’s unwillingness to halt its activities in the face of ever-tightening sanctions “cannot be accepted as normal.”

As such, Mcmanus said the Islamic Republic appeared to be using the ploy of deliberately dragging out talks with world powers on its uranium enrichment program and other nuclear developments.

Tehran, he warned, is committed to “deception, defiance and delay,” the Voice of America reported.

Iran is adding thousands of advanced centrifuges to further enrich uranium into nuclear fuel, Tehran announced Sunday. Some 3,000 centrifuges are being built, according to the report by Iranian state-run media, which said the equipment is being installed at the Natanz nuclear plant.

IAEA chief Yukiya Amano was forced to agree, having said on Monday that without more cooperation from the Islamic Republic, his own inspectors could not conclude that all its nuclear plants were working towards a peaceful goal.  The U.N. agency’s inspectors were refused entry to Iran’s Parchin military site, which is suspected to contain technology aimed at producing a nuclear warhead.

High-level negotiations between Iranian and international experts are scheduled to be held in Istanbul on March 18, followed by talks between top negotiators beginning on April 5.

Iran has denied that it is producing atomic weaponry and insists its nuclear development activities are dedicated to peaceful domestic purposes. But its uranium enrichment program is galloping ahead despite numerous sanctions imposed by the international community. Uranium has already been enriched to a 20 percent-plus level, which is possible for military use and can be employed as fuel for a crude atomic weapon.

Both the U.S. and Israel have repeatedly expressed concern that Iran is developing a nuclear weapon of mass destruction. Iranian leaders have often threatened to annihilate the State of Israel in vitriolic speeches made on various nationalistic holidays.

Israel’s Prime Minister Binyamin Netanyahu has also underscored to the world community that under no circumstances will Jerusalem allow Iran to complete development of a nuclear weapon and pose an existential threat to the Jewish State.