The United States regretted Iran's "failure" to reach an agreement with the International Atomic Energy Agency (IAEA) regarding the additional inspection on its nuclear facilities, the White House said on Wednesday.

"We regret the failure of Iran to reach an agreement this week with the IAEA that would permit the agency to fully investigate the serious allegations raised in its November report," White House spokesman Jay Carney told reporters.

While noting that the UN nuclear watchdog maintains regular access to both of Iran's enrichment facilities at Qom and Natanz, Carney said that the agency was seeking additional access to sites where Iran is suspected of conducting work related to weaponization activities.

"So, unfortunately, it's another demonstration of Iran's refusal to abide by its international obligations," he said.

Carney's remarks came after Yukiya Amano, director of IAEA, said Wednesday that no agreement was reached with Iran over its nuclear issue during the recent two-day visit by the agency' s team to Tehran.

Amano described Iran's refusal to allow access to Parchin as " disappointing." The agency believed Parchin is where Iran's suspicious weapon-related nuclear activities are carried out.

Carney said the United States will continue to evaluate Iran's response to the letter sent by EU foreign policy chief Catherine Ashton regarding the resumption of talks with world powers on Iran 's nuclear issue.

But he stressed that "this particular action by Iran suggests that they have not changed their behavior when it comes to abiding by their international obligations."

The IAEA published a report in November alleging that Iran has engaged in nuclear bomb-related activities. Tehran firmly rejected the report, calling it "imbalanced, non-professional and politically-motivated."

Since then, the United States and the EU have dramatically increased their economic and diplomatic pressure on the Islamic republic, which resulted in the height of tensions between Iran and the West.