Iran has accelerated efforts to develop a long-range ballistic missile, despite tough international sanctions imposed a year ago, the Israeli newspaper Haaretz has reported, citing an unpublished report by U.N. experts.

At the same time, The Jerusalem Post quoted another U.N. report as saying Iran conducted unannounced test-firings of two of its most advanced missiles, the Shibah-3b and the Sejjil-1, in February.

These accounts coincide with a third U.N. report, by the International Atomic Energy Agency, dated May 24 that indicated the Iranians may be close to producing a nuclear warhead that could be carried by their intermediate-range ballistic weapons.

IAEA Director General Yukiya Amano said in the nine-page report his information was Iran has tested and manufactured the shaped explosives used with enriched uranium to create the critical mass that generates a nuclear explosion.

He also cited information that Iran had redesigned the nose cone of the Shehab-3 so it could carry a nuclear warhead rather than one containing conventional high explosives.

Haaretz said the report was produced by a panel of experts convened by U.N. Secretary-General Ban Ki-moon a year ago after the U.N. Security Council imposed a new round of harsh economic sanctions on Iran in an effort to force Tehran to halt its nuclear program.

The report was completed several months ago but hasn't been released, apparently because of pressure from China, a permanent member of the Security Council which has been accused of aiding Iran's nuclear and missile programs.

According to U.S. State Department cables released by WikiLeaks earlier this month, a Malaysian company with links to Iran, Electronics Component Ltd., tried to buy gyroscopes for missiles from China's VibTel Industrial.

The State Department asked China to block the sale in December 2009.

The Americans claimed ECL was linked to Iran's Shahid Hemmat Industrial group, "which is Iran's primary developer of liquid propellant ballistic missiles, and Heavy Metal Industries, a front company for the tactical missile developer Ya Mahdi Industries."

Shahid Hemmat, along with Iran's Sanan Industrial Group, manufactures the Shehab-3 under the umbrella of the state-owned Defense Industries Organization of Iran.

The liquid-fuel, single-stage Shebab-3 medium-range ballistic missile has a reported range of 1,200 miles, capable of hitting the Arab states of the Persian Gulf and Israel.

More advanced variants, the Shehab-4 and Shehab-5 are intended as intercontinental ballistic missiles with anticipated ranges of up to 3,125 miles.

The solid-fuel, two-stage Sejjil-2, which is more advanced and still under development, has a reported range of 1,500 miles. It was first test-fired May 20, 2009, with an upgraded version launched Dec. 16, 2009.

The U.N. report covered by Haaretz said Iran recently tested Sejjil-1 and Shebab-3 on three occasions in a six-month period, a substantially accelerated test program.

Top Israeli missile specialist Uzi Rubin, who said he has read the report, said the information of the Iranian testing was reliable to the best of his knowledge.

Rubin, head of Israel's Missile Defense Organization in 1991-99 and who oversaw development of Israeli Aerospace Industries' Arrow anti-missile defense system, described the tempo of the Iranian testing as "amazing in scope."

The report said U.N. sanctions were impeding Iran's drive to develop long-range missiles as well as nuclear arms.

But it warned: "Iran's circumvention of sanctions across all areas, in particular the use of front companies, concealment methods in shipping, financial transactions and the transfer of conventional arms and related materiel, is willful and continuing …

"In the area of ballistic missiles (Iran) continues to test missiles and engage in prohibited procurement."

The Post said the February test-firings "were not reported at the time by the Iranians, or by the United States or Israel, both of which track such missiles launches."

No explanation for this was offered but Tal Inbar, head of Israel's Space Research Center, said the tests "were significant since Iran was making efforts to hide its ballistic missile program."

Western analysts have been saying Iran still has a long way to go to develop and test intermediate- and long-range weapons, hampered by the imposition of controls on technology transfers from Russia and Ukraine.

The general conclusion was that Iran wouldn't be able to deploy advanced Sejjil variants for five years. It's not clear if that has changed.