Andrew Selth is a research fellow at the Griffith Asia Institute.

The US Treasury's 'designation' of Lieutenant General Thein Htay, Chief of Burma's Directorate of Defence Industries (DDI), for purchasing military goods from North Korea, surprised many. After Barack Obama's visit to Burma in November 2012, when he was assured by President Thein Sein that such activities would cease, concerns about Naypyidaw's shadowy relationship with Pyongyang had seemed to fade.

In March, some suspect dual use materials from North Korea were seized by Japan, but nothing seemed to come of it. And North Korea did not rate a mention in the official statements and learned commentary related to President Thein Sein's return visit to Washington in May. The State Department Fact Sheet issued after the visit was all good news.

Yet US concerns about Burma's military links with North Korea have never gone away.

Before Obama's visit to Burma, Naypyidaw's relationship with Pyongyang was the subject of considerable concern. Washington tended to discount a clandestine nuclear weapons program but remained worried about the possible sale to Burma of ballistic missiles and/or missile production facilities. In April 2012, a senior State Department official told Congress that this was 'a top national security priority'.

During the Obama visit the Burmese Government announced that it would cut its military ties with North Korea. It stated that it had not and would not violate UN Security Council resolutions 1874 of 2009 and 1718 of 2006, both of which banned arms sales from North Korea. Burma also reiterated its commitment to the Nuclear Non-Proliferation Treaty, a claim that has since been accepted by Washington.

Following the Obama visit, and assurances from several Burmese officials that links with North Korea had indeed been severed, the issue dropped from sight. There were warnings from a few critics of the US rapprochement with Burma, but it was almost as if the matter had been resolved. A survey of official US statements over the past year, however, suggests that Burma's relationship with North Korea has continued to weigh on Washington's mind:

Looking back over these statements, it would appear that the US has tried to keep up public pressure on Naypyidaw — as it has doubtless been doing in private — but it has not allowed its concerns over continuing Burmese links with North Korea to interrupt the development of bilateral relations. This represents a softening in the US position since Hillary Clinton's December 2011 visit to Burma.

This policy shift may account for the fact that sanctions have been imposed on a single department of Burma's armed forces and an individual army officer. The recent Treasury document specifically states that it is not targeting the Burmese Government, which 'has continued to take positive steps in severing its military ties with North Korea'. It also refers to Naypyidaw's undertaking in 2012 to abide by the relevant UNSC resolutions.

That formulation may satisfy diplomatic etiquette, but it is difficult to see how LTGEN Thein Htay or the DDI could maintain links with a foreign power without the knowledge of the armed forces leadership, and probably the president. It is also unlikely that DDI's acquisitions from North Korea have not been in formal breach of UNSC resolutions 1874 and 1718. If the transactions were benign, why the strong US response?

As Network Myanmar's Derek Tonkin has pointed out, the Treasury statement did not say when the offences took place, or what arms were involved. However, a US spokesman has revealed that the Treasury Department has had concerns about Thein Htay since last November, when he led a Burmese delegation to Beijing. There he met North Korean officials and signed an agreement to expand bilateral military ties.

Senator Richard Lugar is no longer around to voice his perennial concerns about secret deals between Pyongyang and Naypyidaw, but Congress has already sounded some warning bells. North Korea was not specifically mentioned, but in June both houses called for greater transparency from the Burmese about military budgets and operations before the US seeks closer engagement with their armed forces.

The Burmese Government has expressed surprise at the recent Treasury announcement, and President Thein Sein's office has claimed not to know the evidence on which the latest US sanctions are based. Only last month, the Speaker of Burma's lower house of parliament reportedly told officials in Washington that Burma's arms trade with North Korea had ceased, and that Naypyidaw was observing the relevant UNSC resolutions.

The latest developments in this saga raise a number of difficult questions. Is LTGEN Thein Htay a maverick, acting alone? Are Burma's armed forces beyond the president's control? Is Naypyidaw trying to squeeze in a few more arms sales and wrap up a secret missile program before cutting its ties with Pyongyang? Is Thein Sein hoping that the US wish to preserve its good relations with Burma will persuade it to turn a blind eye?

Once again, observers are left bemoaning the lack of hard information, not only about Burma's shadowy relationship with North Korea, but also what drives the decisions of policy makers in Naypyidaw and Pyongyang — and Washington.