"That's one of a number of concerns that we have in regards to Iran. We have continued to work with the IAEA and the international community to make sure that there are more intensive inspections of Iran and this particular weapons program," Scott McClellan told reporters in this Texas town where President George W. Bush is vacationing.
The statement came a day after The Los Angeles Times reported that Iran is striving to become the world's next nuclear power and appears to be in the late stages of developing the capacity to build a nuclear bomb.
"It is a matter that remains a serious concern. We're working with the international community. We're working with the IAEA to make sure that they do not continue on this course, which is unacceptable," he said.
The United States is "working with the international community to keep pressure on Iran to open up to more intensive of inspections. And we will continue doing that, but we have a lot of concerns about the pursuit of nuclear weapons," he added.
IAEA experts began crucial talks in the Iranian capital Monday on whether or not Tehran would accept snap inspections of its nuclear sites, as the conservative camp stepped up calls for Iran to resist US-led pressure.
Three legal experts of the IAEA, the UN's nuclear watchdog, were holding talks with Iranian counterparts, said the spokesman of Iran's nuclear energy organization, Saber Zaimian, quoted by the Iranian state news agency IRNA.
The Los Angeles daily said that Iran's nuclear program was much closer to producing a bomb than Iraq ever was, perhaps in as little as two or three years, according to some experts.