The White House expressed "grave concerns" Friday over Iran's nuclear program, saying there would be "consequences" if Iran fails to comply with requirements of the United Nations and the UN nuclear watchdog International Atomic Energy Agency (IAEA).

"The United States echoes the grave concerns expressed by the European Council today regarding Iran's nuclear program," White House spokesman Robert Gibbs said.

Gibbs said Iran has not taken advantage of opportunities to build trust and confidence. Instead, it has increased the international community's concerns about its nuclear program.

He said if Iran continues to fail to comply with the United Nations' and IAEA's requirements, "there will be consequences."

The spokesman said "the offer of constructive engagement is still on the table," calling Iran to uphold its international obligations, and return to negotiations with the five permanent members of the UN Security Council -- Britain, China, France, Russia, and the United States -- plus Germany.

Last month, the IAEA censured Iran for hiding an enrichment plant in Qom. Days later, Iran announced it would increase its enrichment program by building 10 new plants.

Earlier in the day, U.S. Secretary of State Hillary Clinton warned Latin American countries of promoting their ties with Iran, saying they should "think twice."

She said on another occasion the international community still wanted to engage with Iran, but was beginning to turn to more pressure, such as sanctions.

The UN Security Council met Thursday to assess Iran's compliance with previous sanctions and heard a report from the sanctions committee on two shipments of Iranian arms bound for Syria that violated the UN arms embargo on Iran.

The United States, France and Britain warned afterwards more sanctions are inevitable if Iran continues to defy United Nations demands, while China and Russia urged for greater patience in continuing negotiations.

The five permanent members of the UN Security Council have agreed to wait until the end of the year before deciding on more sanctions against Iran.

Iran maintains it has the right to generate nuclear energy for civilian purposes. But Western powers suspect Iran of attempting to build nuclear weapons.