BANGKOK — Thailand’s prime minister sought Thursday to quiet international concerns about the possible expulsion of 4,000 ethnic Hmong to Laos, amid protests from the U.S. and human rights groups who fear they could face persecution. Prime Minister Abhisit Vejjajiva declined to say when the Hmong would be deported but indicated it could happen soon. "We will act according to the law, and we will be very careful,” Abhisit told reporters. "We have measures to take care of this without human rights violations.” The Hmong, an ethnic minority group from Laos’ rugged mountains, are being held at a camp in northern Phetchabun province. They say they fear political persecution in Laos, where many Hmong fought on the side of a pro-U.S. Lao government in the 1960s and 1970s before the communist takeover of their country in 1975. Laos in the past has denied the Hmong are Lao citizens, describing them as Thailand’s problem. Thai authorities say the group of Hmong in Phetchabun are not legitimate refugees and have entered the country illegally. The two countries reached an agreement earlier this year to repatriate the group. "According to the agreement, we will send them back at the proper time,” Abhisit said. The U.S. State Department expressed concern for the Hmong on Thursday, noting that in the past the Thai government has said that many Hmong are in need of protection.