US urges probe into Thailand attacks

"As allies and close friends of the Thai people, we are profoundly saddened by the deaths and injuries that have shaken the country," Kerry said in a statement.

"I call upon Thai authorities to investigate these attacks swiftly and bring those responsible to justice," he said, adding "violence is not an acceptable means of resolving political differences."

Thai opposition protesters seeking to force Prime Minister Yingluck Shinawatra from office said Friday they would abandon most of their rally sites in the capital, ending their self-styled "shutdown" of Bangkok, which has lasted some four months.

The move follows increasingly frequent gunfire and grenade attacks targeting the protest sites, mostly at night.

Violence linked to the rallies has left 23 people dead and hundreds wounded in recent weeks, including four children killed in two separate grenade and gun attacks on opposition rallies last weekend.

"As a father and grandfather, the death of several innocent children is particularly horrifying, and must at last be a wake-up call to all sides to refrain from violence, exercise restraint, and respect the rule of law," said Kerry.

He insisted that the United States does not take sides in Thailand's politics, saying it was up to the Thai people to resolve their differences.

But he highlighted US concern about "the employment of other tactics that undermine Thailand's democratic values and processes, inhibit compromise, and further exacerbate political tensions."