Regional powers have for years tried — with a mix of aid offers and punitive sanctions — in vain to stop Pyongyang pressing ahead with a nuclear weapons program it argues is a necessary defense against a hostile United States and South Korea with which it still has no peace treaty to formally end the 1950-53 Korean War. Kim Kwan-jin offered no evidence to back his assertion but said the North had had enough time for such a development.

“It has been quite a while, enough time for them to have succeeded in miniaturization,” he told a parliamentary defense committee.

If true, it would mark a key advance in the North’s drive to develop a functioning nuclear weapon though that threat appears to be potential rather than actual.

It detonated nuclear devices in 2006 and 2009 but neither was considered by weapons experts to have been successful, though they say the impoverished state has enough fissile material for up to 10 nuclear weapons.

It is believed to be preparing a third test at a test site on its east coast.

The North has also been working, so far with little success, to build a missile capable of delivering a nuclear weapon across the Pacific, as far as the United States.

Talks with major powers on its nuclear weapons program have been on ice for more than two years though the North has signaled it wants them to resume.

However, both the United States and key allies South Korea and Japan have been reluctant to head back into negotiations which in the past have rewarded the North for little if anything in return.

Meanwhile, The US Navy intercepted a North Korean ship suspected of carrying an illegal shipment of missile parts to Myanmar two weeks ago, the New York Times reported on late Sunday, citing American officials. The North Korean cargo ship was forced to return home after a standoff at sea and several days of diplomatic pressure from Washington and Asian nations, the newspaper reported.

Officials for the US Navy and the State Department were not immediately available for comment late on Sunday.

UN sanctions imposed on North Korea after it conducted nuclear tests include a ban on trade in nuclear and missile technology with North Korea. A UN resolution adopted last year authorized UN member states to inspect North Korean sea, air and land cargo.

According to the Times, the destroyer USS McCampbell caught up with the cargo ship M/V Light south of Shanghai on May 26 after American officials began tracking the vessel, which was believed to have been involved in previous illegal shipments.

The destroyer asked to board the vessel under authority given by Belize, but the North Koreans refused, the Times said.

An American official told the newspaper the ship was North Korean but flagged in Belize. Authorities in Belize gave the United States permission to inspect the ship, the newspaper said, citing American officials.