PHNOM PENH (AFP) -- Cambodian riot police Tuesday broke up a protest by dozens of Buddhist monks angered at Hanoi's treatment of clergy as Vietnamese President Nguyen Minh Triet arrived for an official visit.

"I won't allow the monks to gather because today I need to ensure security for the Vietnamese president, who is the king's guest," said Phnom Penh police chief Touch Naruth.

Triet, the third Vietnamese leader to visit Cambodia in two years, arrived at the invitation of King Nodorom Sihamoni and is expected to discuss a wide range of projects, including power, transport and tourism efforts, the Vietnam News daily reported.

Two-way trade between the neighbors has grown by almost 40 percent a year during the past decade and reached 900 million dollars in 2006, according to Vietnamese state media.

Communist forces in the two former French colonies were allies during the Vietnam war that ended in 1975, but Vietnam invaded Cambodia in 1978, ousted Pol Pot's Khmer Rouge regime and occupied the country for a decade.