Szubin said the Bush administration "has made clear that we will continue to take action against the military junta and those who prop it up so long as human rights violations continue and democracy is suppressed.''
The treasury also named Aung Thet Mann, one of Tay Za's directors and the son of General Thura Shwe Mann, a senior government official and a member of the ruling State Peace and Development Council.
"Tay Za has used his business relationship with Aung Thet Mann to win favourable business contracts from the Burmese junta," it said in a statement.
"The actions of Than Shwe and his associates remain unacceptable to all those who value freedom"
White House Press Secretary
The US started imposing targeted sanctions against Myanmar after the government's bloody crackdown on anti-government protesters in September last year.
The new sanctions against individuals and firms entail freezing their assets under US jurisdiction and barring Americans from conducting business with them at the risk of heavy fines and prison sentences.
On Tuesday the White House condemned Myanmar's rulers for continuing to arrest activists and Buddhist monks, and for barring UN special advisor Ibrahim Gambari from returning to Myanmar.
"The actions of Than Shwe and his associates remain unacceptable to all those who value freedom," Dana Perino, the White House press secretary, said in a statement, referring to the continued house arrest of Aung San Suu Kyi, the opposition leader and Nobel peace laureate.
The statement added: "The president has said that the United States would continue to review our policies and consider additional measures if Than Shwe's junta did not end its brutal oppression of the Burmese people."
The latest designation of sanctions will freeze any assets of family members of the military leadership and other key individuals and businesses within Tay Za's financial network.
The companies on the treasury blacklist include Myanmar Avia Export Company Ltd, Ayer Shwe Wah Company Limited and Pavo Aircraft Leasing Pte Ltd in Singapore.
Four wives of senior government officials were also among the targets – Khin Lay Thet, the wife of General Thura Shwe Mann; Myint Myint Ko, the wife of Construction Minister Saw Tun; Tin Lin Myint, the wife of Lieutenant-General Ye Myint; and Myint Myint Soe, the wife of Foreign Affairs Minister Nyan Win.