Four Cambodian activists jailed for defaming the government have been released on bail as what is described as a "present" to visiting U.S. Assistant Secretary of State Christopher Hill, who welcomed the release but said the international community must watch to make sure human rights are protected in Cambodia.

Kem Sokha from the U.S.-funded Cambodian Center for Human Rights celebrates with his supporters outside Prey Sar prison

Hundreds of supporters welcomed four activists, just freed from jail, as they were carried into the headquarters of the Cambodian Center for Human Rights.

Two leaders of the center, Kem Sokha and Pa Nguon Teang, as well as journalist Mam Sonando and the head of a teacher's union, Rong Chhun, were released on bail Tuesday. They had been arrested several weeks ago on charges of criminal defamation for criticizing the government's policy on the border with Vietnam.

Cambodian Prime Minister Hun Sen asked that the four activists be granted bail after he met with U.S. Assistant Secretary of State Christopher Hill Tuesday in Phnom Penh.

A government official, Om Yentieng, told reporters Tuesday the activists were released as a "present" for Hill.

Hill called the release a step in the right direction, but described Cambodia as a nation where political problems occur when the international community is not paying attention. He said the United States will keep a watchful eye on Cambodia and remains committed to helping it develop democracy.

"Cambodia is still very much a country in transition, and I think it's very important that we pay attention to what's going on," said Hill, "and that we'll have to be very mindful of the human rights situation here, and we should be doing all that we can to encourage improvement in that situation."

Hill, in Cambodia for the opening of a new U.S. Embassy building, is on a tour that includes Tokyo, Seoul, Beijing and Kuala Lumpur.

His comments echoed the strong concern voiced by the international community over the arrests of several human rights activists and critics of the government in the past few months.

The government says it sued the activists to defend its image over a controversial border treaty signed with Vietnam, but officials say they did not order the men arrested.

Critics of the government say the prime minister is trying to quash his opposition and consolidate control over the country.