WASHINGTON (AFP) - The United States said Tuesday that it did not believe ally Thailand's army had staged a coup but urged the military to respect democratic institutions.

"Martial law, the declaration of that, is allowed for in the Thai constitution," State Department spokesman Jen Psaki told reporters after gun-toting troops deployed across Bangkok.

"The army has stated publicly that it would be a temporary action. We expect them to abide by their commitment," Psaki said.

Psaki said that the United States has been in regular contact with the Thai military and was "encouraging calm, encouraging protection of civil liberties and freedom of speech and freedom of media."

Under domestic law, the United States would be forced to impose sanctions if it determines that a foreign military has carried out a coup. The United States briefly suspended cooperation with the Thai military after it ousted tycoon Thaksin Shinawatra as prime minister in 2006, setting off prolonged political turmoil in the kingdom.

Danny Russel, the top US diplomat on East Asia, called on Thailand's caretaker government to go ahead with promises for fresh elections on August 3.

"We want to see the early restitution of full democracy in Thailand and respect for Thailand's democratic institutions," Russel told the House Foreign Affairs Committee.

"We think that requires free and fair elections that enable the Thai people freely to express their political will," Russel said.

Thailand is the oldest US ally in Asia, and the United States has been careful about appearing to take sides in the turbulent politics of the kingdom, which has seen 18 coups or coup attempts since it became a constitutional monarchy in 1932.

The military intervened after nearly seven months of protests that have left 28 people dead and hundreds wounded.

But the military kept in place the caretaker government, which was installed earlier this month after a court dismissed prime minister Yingluck Shinawatra, the sister of the exiled Thaksin.