Thai police are monitoring departures from a popular resort island after the battered bodies of a British man and woman were found on a beach.

The deaths on the small southern island of Koh Tao are being investigated as murders. The victims were discovered early Monday partially undressed with severe injuries to their heads, and a hoe with blood on it was found near the bodies, police said.

The two Britons, both in their early 20s, were last seen hanging out with friends at a bar in the early hours of Monday before leaving together, said Maj. Gen. Kiatthipong Khaosumarng, the provincial police chief.

Police want to interview a number of people seen on surveillance camera footage from the bar, he said, adding that police have ruled out robbery as a motivation for the attack.

Authorities believe that the culprit or culprits could still be on the island. They have circulated photos of 10 people they are looking for among local authorities, said Col. Prachum Ruangthong, the police chief of the local precinct.

A team of police officers in plain clothes are keeping watch at the main pier on the island, he said.

A regional police official had earlier told CNN that people had been prevented from leaving Koh Tao, but Prachum said that wasn't the case.

The deaths have shaken residents on the idyllic island, which takes up only 21 square kilometers (8 square miles) amid bright blue waters in the Gulf of Thailand. Authorities said it was the first homicide case on Koh Tao in at least eight years.

The island is popular among tourists for its diving locations, white sand beaches and vibrant nightlife.

Police said that interviews with friends of the victims indicated that the two Britons may have only recently met while on the nearby larger island of Koh Phangan before traveling to Koh Tao for a party excursion.

The British Consul arrived in Koh Tao on Tuesday, the British Embassy in Bangkok said.

"The Embassy is urgently seeking information from the local authorities and Consular staff stand ready to provide assistance to friends and family at this tragic time," it said in a statement, declining to give any further details on the case.

While the victims' names have been widely reported, the Embassy wouldn't tell CNN if their families have been notified yet.

Thai authorities said they planned to send the victims' remains to Bangkok for forensic tests.

(CNN)