BANGKOK — U.S. Secretary of State Hillary Rodham Clinton said today that the Obama administration is concerned by the possibility that North Korea, with a history of illicit sales of missiles and nuclear technology, is developing military ties to Myanmar.

She did not refer explicitly to a nuclear connection but made clear that the matter is disconcerting.

"We know there are also growing concerns about military cooperation between North Korea and Burma which we take very seriously," she said when asked about it at a news conference in the Thai capital. Myanmar, also known as Burma, is run by a military regime.

"It would be destabilizing for the region, it would pose a direct threat to Burma's neighbors," she said, adding that as a treaty ally of Thailand, the United States takes the matter seriously.

Later, a senior administration official said that Washington is concerned about the possibility that North Korea could be cooperating with Myanmar on a nuclear weapons program, but he added that U.S. intelligence information on this is incomplete. The official spoke on condition of anonymity because of the sensitive nature of the matter.

Another administration official, speaking under the same ground rules, said one reason for concern on the nuclear front is the evidence that North Korea helped Syria clandestinely build a nuclear reactor, which was destroyed in an airstrike in 2007 by the Israeli air force.

The United States, in a joint effort with South Korea, Japan, China and Russia, is attempting to use U.N. sanctions as leverage to compel North Korea to return to the negotiating table over its nuclear program. A major element of the international concern about North Korea is the prospect of its nuclear proliferation, which could lead to a nuclear arms race in Asia and beyond.

At the news conference, Clinton held out the possibility of enticing North Korea back to negotiations on reversing its nuclear program.

"We think that there is a different path for North Korea to follow, that there is an opportunity which is theirs for the taking, but they have to be willing to change their behavior and agree to de-nuclearize North Korea, which would mean that the entire Korean peninsula is denuclearized, and we stand ready to respond if we get any signal that there would be a serious commitment to doing that," she said.

The senior administration official said the U.S. has not yet received any such signal from Pyongyang. For now, he added, the focus of the administration's effort is on persuading other countries to vigorously enforce a new set of U.N. sanctions against North Korea following its latest missile tests. In order to get as many countries as possible to join the enforcement effort, the administration believes it needs to publicly hold out the possibility of a new set of incentives for North Korea in the event it agrees to nuclear talks.

Clinton spoke to reporters after meeting with Thai Prime Minister Abhisit Vejjajiva at the outset of a three-day visit to Thailand. She is scheduled to fly to the Thai seaside resort of Phuket on Wednesday to attend an international meeting on Asian security. Myanmar and North Korea are expected to have representatives there, but Clinton has no plans to meet with them, officials said.

The senior administration official held out the possibility that a member of Clinton's staff might have contacts with representatives of Myanmar or North Korea during the Phuket conference. The U.S. has diplomatic relations with Myanmar but not with North Korea.

Clinton said she would, as previously announced, sign ASEAN's seminal Treaty of Amity and Cooperation to which more than a dozen countries outside the 10-nation bloc have already acceded. The U.S. signing will be done on the executive authority of President Barack Obama and does not require congressional ratification, the senior administration official said. The administration of President George W. Bush declined to sign the document; Obama sees it as a symbolic underscoring of the U.S. commitment to Asia.

Clinton sharply criticized the military rulers of Myanmar for human rights abuses, "particularly violent actions that are attributed to the Burmese military concerning the mistreatment and abuse of young girls." She said an Obama administration policy review on Myanmar is on hold pending the outcome of the trial of democracy leader Aung San Suu Kyi, who is accused of violating the terms of her house arrest. The Noble Peace Prize laureate faces up to five years in prison if convicted, as expected.

"Our position is that we are willing to have a more productive partnership with Burma if they take steps that are self-evident: end the violence against their own people including the minorities that they have been focused on in the last months, end the mistreatment of Aung San Suu Kyi and the political prisoners in detention who have been rounded up by the government and other steps that Burma knows it could take," she said.