The US must appoint an envoy to Burma “without delay” in light of allegations that the pariah state is developing a nuclear weapons programme and has traded military hardware with North Korea, a senior US senator has said.

In a letter yesterday to US secretary of state Hillary Clinton, Jim Webb, who last week cancelled a trip to Burma after the allegations surfaced, called on Washington to examine “objectively and factually…and in a timely manner” the allegations.

He said that the appointment of an envoy was a requirement of the 2008 Tom Lantos Block Burmese JADE Act, but that the position remained empty. An envoy, he said, would promote “multilateral sanctions, direct dialogue with the [Burmese junta] and democracy advocates, and support for nongovernmental organizations operating in Burma and neighbouring countries”.

The US ambassador to Thailand, Eric John, was given a “strong recommendation” by Webb as someone fit for this role, largely for his knowledge of East Asian affairs, which includes “long experience in dealing with the North Korean regime on issues that might be similar to those we will be facing in Burma”.

The US appears to take the warming relationship between Burma and North Korea as a real threat, but has remained coy about the extent of its knowledge on the relationship: Webb mentioned in his letter reports about a weapons shipment from North Korea to Burma this year, which the US is believed to have known about, but added that the state department was yet to publicly clarify the details.

State department spokesperson Philip Crowley told reporters yesterday that he and Clinton hadn’t yet seen the letter, but asserted that Burma remains a country “of significance” to the US. However he declined to answer whether the appointment of an envoy was a viable option for the US, saying only that Washington was “watching closely” the relationship with North Korea.

Part of the reason for US concern is its waning influence in Southeast Asia, which has allowed China to strengthen economic and political ties with, among others, Burma and North Korea. Huge gas sales to China have largely financed Burma’s weapons programme and have supported clandestine trade with Pyongyang, which appears to have evaded a tight UN arms embargo.

In his letter, Webb lamented the silence from the state department regarding recent weapons exports from North Korea to Burma; it is alleged that a ship offloaded cargo at a Rangoon port around April this year, although more specific details have not been released.

He said that he and his staff “worked for weeks to seek public clarification of this allegation, but the State Department provided none”. But as the results of a five-year investigation by DVB into Burma’s nuclear ambitions and its ties with North Korea began to surface last week, Webb cancelled what would have been his second visit to Burma.