TOKYO — The State Department is advising caution for all U.S. citizens in Thailand, following the declaration of martial law throughout the country Tuesday.

The declaration came a day after Thailand’s caretaker prime minister said he would not resign, amidst ongoing political protests.

“You are advised to avoid areas where there are protest events, large gatherings, or security operations and follow the instructions of Thai authorities,” according to the U.S. Embassy in Bangkok’s statement.

“U.S. citizens are cautioned that even demonstrations that are meant to be peaceful can turn confrontational and escalate into violence.”

The embassy also encouraged Americans in Thailand to register with the embassy, either online or through consulate services.

The warning follows a travel alert issued by the embassy May 16. The alert did not advise against nonessential travel, but it did cite risks, especially in Bangkok, “due to ongoing political and social unrest.”

Thai army officials told reporters Tuesday that the declaration of martial law was a not a coup, an action taken repeatedly by the military since Thailand became a constitutional monarchy in 1932.

In Washington, State Department officials expressed concern over the martial decree.

“We expect the army to honor its commitment to make this a temporary action to prevent violence, and to not undermine democratic institutions,” State Department spokeswoman Jen Psaki said in a statement Tuesday.

The last coup came in 2006, when the military forced out Prime Minister Thaksin Shinawatra. Thaksin had popular support, especially in the countryside, but also faced a strong opposition movement and accusations of corruption.

On May 7, Yingluck Shinawatra, Thaksin’s sister, was forced out as prime minister after a court found her guilty of abuses of power.

The U.S. military maintains a close relationship with Thai military officials. Each year, Thai officials host the multinational Cobra Gold exercise, which welcomes thousands of U.S. servicemembers.

On May 12, senior Navy leaders hosted Royal Thai Navy officials aboard the Japan-based USS Blue Ridge. A Navy news release cited Thailand as “America’s oldest ally in Asia,” tracing relations back to a treaty signed between the U.S. and the Kingdom of Siam in 1833.

slavin.erik@stripes.com

Twitter: @eslavin_stripes