* Anadarko reacts to mystery militant unrest
* Staff ordered not to leave site of planned LNG plant
* At least 39 people killed since May, HRW says (Releads with Anadarko action)
By Ed Cropley
JOHANNESBURG, June 19 (Reuters) - U.S. petroleum company Anadarko has placed staff working on a liquefied natural gas (LNG) plant in northern Mozambique under "lock-down" due to the threat from suspected Islamist militants in the area, a regional security consultant said on Tuesday.
Anadarko, which is looking to raise a record $14-$15 billion for the plant, said last week it was monitoring the situation after a spate of beheadings and kidnappings but declined to comment on specific security issues.
The consultant, who is familiar with the security situation, said the firm had prevented its workers from going beyond the perimeter of the planned plant on the coast of Cabo Delgado province, abutting the border with Tanzania.
"They can't leave the site," the consultant said.
Besides Anadarko, Italian energy giant Eni is piling into northern Mozambique to develop gas fields in the offshore Rovuma Basin, believed to hold 85 trillion cubic feet of natural gas - enough to supply Germnay, Britain, France and Italy for nearly two decades.
The first attacks by suspected Islamist militants came in October, when locals reported gangs armed with machetes attacking police stations, torching villages and executing religious leaders.
Human Rights Watch (HRW) said on Tuesday at least 39 people had been killed and more than 1,000 displaced since May. The United States and Britain have advised their citizens to steer clear of the area.
Security consultants and domestic media have described the attackers as members of Al-Sunna wa Jama’a, an unknown Islamist group. Locals have also referred to the attackers as "Al-Shabab", although there are no known links to the Somali group of the same name.
People in Cabo Delgado told HRW attackers had burned a mosque and beheaded an Islamic leader in a June 5 attack in which hundreds of homes were torched and scores of cattle slaughtered.
The New York-based rights group also accused the Mozambique security forces of an indiscriminate and heavy-handed response, citing one military unit commander who said his troops would not "waste our time" handing over suspects.
"If we find them in the bush, we will kill them there," the soldier was quoted as saying.
A government spokesman was not immediately available for comment.
Mozambique has no history of Islamist militancy and authorities have been reluctant to ascribe the attacks to Islamists. About 30 percent of Mozambique's 30 million people are Roman Catholics, while 18 percent are Muslim. (Additional reporting by Joe Brock Editing by Catherine Evans and Andrew Heavens)