Arms control experts are questioning the findings of a U.S. university professor and his students who say China's nuclear arsenal may be many times larger than official estimates.

The study examines China's vast network of tunnels designed to hide the country's missile and nuclear arsenal.

Students at Georgetown University, led by their professor, Philip Karber, say China could have up to 3,000 nuclear warheads hidden in the tunnels, far higher than the current official estimates of around 250.

Karber's report has sparked controversy among experts on China and nuclear weapons. The report has not been released publicly, but it has been circulated among U.S. defense officials, and its finding have been published in U.S. media reports.

Karber, who is a former senior Pentagon official, did not respond to requests from VOA for an interview. But Gregory Kulacki, a senior analyst at the Union of Concerned Scientists, told VOA he considered the Georgetown group's research methods to be irresponsible.

“What I am angry about, and where I think there is this incompetence and laziness involved here, is that neither Dr. Karber, nor his students, went to the original source of the claim to evaluate it. They simply collected rumors on the Internet, published them on a slide, and made a sensational claim about the size of the Chinese article to a group of experts in Washington D.C. That is not responsible scholarship. It's rumor-mongering, pure and simple.”

But Kulacki said he was not necessarily defending the official Pentagon estimate of about 250 weapons in the Chinese nuclear arsenal.

The one thing I would agree with Dr. Karber on is, we don't know. That's why we need to be careful, and serious about investigating this question.”

The study by the Georgetown students used Internet-based sources such as satellite images, blogs and military journals. It concluded that the growing number of tunnels that China is digging and its increasing deployment of missiles suggests that the country has more nuclear warheads than previously thought.

However, critics of the report say that more tunnels in China does not necessarily mean more nuclear weapons.

Karber acknowledged to the Washington Post that he does not know how many nuclear weapons China really has. But he said that U.S. experts in the arms-control community also do not know.