PHNOM PENH (Reuters) - Cambodian Prime Minister Hun Sen called on the United States on Friday to withdraw Peace Corps volunteers in an escalating row over accusations that U.S. agents conspired with an opposition leader to plot treason.

FILE PHOTO: Cambodia's Prime Minister Hun Sen, who is also president of the ruling Cambodian People's Party (CPP), arrives before a ceremony to mark the 66th anniversary of the establishment of the party, at Koh Pich island in Phnom Penh, Cambodia, June 28, 2017. REUTERS/Samrang Pring

Hun Sen was responding after the U.S. embassy in Phnom Penh issued a travel warning that urged citizens to show caution amid “anti-American rhetoric by officials”.

“Are you scaring Cambodians?” Hun Sen said of the United States in an address to garment workers at factories which export much of their production to the United States.

“Are you prepared to invade Cambodia and that’s why you told Americans to be careful? It’s good if you pull out the Peace Corps,” Hun Sen said.

The U.S. embassy declined to comment. It has previously dismissed the accusations of collusion with opposition leader Kem Sokha and called for his release.

On Friday, the embassy was swearing in 71 new volunteers from the Peace Corps, which sends Americans abroad to help with local projects with the stated goal of promoting mutual understanding.

Hun Sen said on Friday that he had ordered an investigation into whether any Americans were involved with Kem Sokha.

Opponents of Hun Sen accuse him of arresting Cambodia National Rescue Party (CNRP) leader Kem Sokha and cracking down on independent media and other critics ahead of a general election next year.

The evidence presented against Kem Sokha is a video recorded in 2013 in which he discusses a strategy to win power with the help of unspecified Americans.

Hun Sen, a close ally of China, has taken a series of measures against U.S. interests this year from ending joint military exercises to expelling a naval aid unit to forcing a U.S.-funded pro-democracy group to leave.

On Thursday, Hun Sen said he was suspending cooperation with Washington to find the remains of Americans killed in the Vietnam War.

According to the U.S Embassy, more than 500 Peace Corps volunteers have served and worked in Cambodia since 2006, providing English teaching and teacher training as well as community health education.

U.S. President John F. Kennedy established the Peace Corps in 1961 to promote world peace and friendship.