Thu Sep 27, 1:59 PM ET

WASHINGTON - The United States on Thursday ordered a freeze on the assets of Myanmar's military leader and 13 other senior officials in sanctions imposed after a crackdown on dissent in the Asian nation.

"We are today imposing sanctions against senior officials of the government of Burma," said Adam Szubin, director of the Treasury's Office of Foreign Assets Control.

Szubin said US President George W. Bush "has made clear that we will not stand by as the regime tries to silence the voices of the Burmese people through repression and intimidation."

The announcement came after Bush said the world must press Myanmar's military rulers to end a violent crackdown on protests and urged the junta to cooperate fully with a UN special envoy.

"I call on all nations that have influence with the regime to join us in supporting the aspirations of the Burmese people and to tell the Burmese Junta to cease using force on its own people, who are peacefully expressing their desire for change," he said in a statement.

Among those designated for sanctions were junta leader Than Shwe, who is minister of defense and chairman of the State Peace and Development Council (SPDC); Vice Senior General Maung Aye, commander of the army and vice chairman of the SPDC; Lieutenant General Thein Sein, acting prime minister and first secretary of the SPDC; and General Thura Shwe Mann, joint chief of staff and member of the SPDC, along with other senior officials and military officers.

Bush spokeswoman Dana Perino said that Myanmar-bound UN envoy Ibrahim Gambari must be able to meet with "all relevant parties" including political prisoners and detained democracy icon Aung San Suu Kyi.

"The world is watching the people of Burma take to the streets to demand their freedom, and the American people stand in solidarity with these brave individuals," the US president said.

"Every civilized nation has a responsibility to stand up for people suffering under a brutal military regime like the one that has ruled Burma for too long," said Bush, who made a direct appeal to Myanmar security forces.

"I urge the Burmese soldiers and police not to use force on their fellow citizens. I call on those who embrace the values of human rights and freedom to support the legitimate demands of the Burmese people," he said.