The head of Iran's nuclear program said Monday his country hopes to begin construction within a year on two uranium enrichment facilities, which it plans to build deep inside mountains to protect them from possible attack.

Ali Akbar Salehi, who is also Iran's vice president, said Tehran intends to use its more advanced centrifuges at the new sites, a decision that could add to growing concerns in the West over Tehran's program because the technology would allow Iran to accelerate the pace of its program.

In November, Iran approved plans to build 10 industrial scale uranium enrichment facilities, a dramatic expansion of the program in defiance of U.N. demands it halt enrichment.

"Hopefully, we may begin construction of two new enrichment sites in the next Iranian year as ordered by the president," the semiofficial ISNA quoted Salehi as saying Monday. The Iranian calendar year begins March 21.

"As of now, our enrichment sites ... will be built inside mountains," Salehi added, according to ISNA.

The decision appears to be aimed at shielding the facilities from possible attack. Israel considers Iran a strategic threat because of its nuclear program, and has hinted at the possibility of a military strike against Iran if world pressure does not halt Tehran's nuclear efforts.

Iran's enrichment of uranium is the central concern of the United States and other nations negotiating with the country over its disputed nuclear program. The technology can be used to generate fuel for power plants and isotopes for medical purposes, but it can also be used to make weapons-grade uranium for atomic bombs.

Tehran insists its enrichment work is only meant for peaceful purposes, but Washington and its allies are suspicious of Iran's intentions and worry the program masks efforts to build a nuclear weapon.

Tehran has already said it may install its more advanced centrifuges at its small enrichment site near the holy city of Qom, which was made public last September. The new centrifuges are more advanced than the decades-old P-1 type centrifuges in use at the country's main enrichment facility at Natanz, in central Iran.

Centrifuges are machines used to enrich uranium — a technology that can produce fuel for power plants or materials for a nuclear weapon. Uranium enriched to a low level is used to produce fuel, but further enrichment makes it suitable for use in building nuclear arms.

The new models will be able to enrich uranium much faster than the old ones — which means Iran could amass more material in a shorter space of time that could be turned into the fissile core of missiles, should Tehran choose to do so.

Tehran produced its first batch of uranium enriched to a higher level earlier this month, prompting the U.S. and its allies to seek new U.N. Security Council sanctions.