(Corrects name in second para to International Institute for Strategic Studies)

By Luke Baker

LONDON, Feb 5 (Reuters) - Nearly 400 militant groups now operate around the world and the greatest proliferation has been in the border regions between Afghanistan, Pakistan and India, an annual military report showed on Tuesday.

The number of violent "non-state" groups has grown about 10 percent in the past year, according to the 2008 Military Balance report by the International Institute for Strategic Studies.

Iraq and India, with more than 30 active guerrilla groups each, are the most volatile countries. The Afghan/Pakistan border and the Kashmir region between India and Pakistan are the worst affected areas, with a total of 65 groups in operation.

"It reflects the changing nature of conflicts over the past 10 to 15 years," said Nigel Inkster, the director of transnational threats and political risk at IISS.

"We're seeing less and less inter-state conflict and more and more intra-state conflict involving a wide variety of armed groups -- the number just keeps on spiralling."

Inkster, a former director of operations with Britain's Secret Intelligence Service, said the fastest growing threat came not from al Qaeda or any of its offshoots in Iraq, but probably Tehrik-a-Taliban, a Pakistani Taliban movement.

Led by Baitullah Mehsud, an ethnic Pashtun tribal warlord, the group has a base in Waziristan, in the Pakistan/Afghanistan border region, and has recently expanded to align itself with global struggles.

"It has its roots in localised issues but very recently they have shown an inclination to link themselves to a wider agenda," Inkster told Reuters.

"Because of the wider ramifications of unrest in the region, the Pakistani neo-Taliban, as it is called, has become a potent and growing threat.

"Mehsud has linked himself formally with the Afghan Taliban and has been quoted about the need to annihilate the United States and Britain, so he is adopting a wider political agenda."

PRIME SUSPECTS

Mehsud and his followers are the prime suspects behind the assassination of Pakistan opposition leader Benazir Bhutto and are believed to have carried out several other suicide bombings in Pakistan, Inkster said.

Because it is a localised, tribal-based group, its numbers are amorphous, expanding when there may be a threat and just as quickly melting away into the rugged landscape of Waziristan.

"In south Waziristan they are actually pretty well established and the Pakistani army can't really take them on full frontal," Inkster said.

Britain and the United States are also home to a wide variety of non-state groups that have recognised ideological or political goals and could turn to violence to carry them out.

As well as the remnants of the Real IRA, Britain has al-Muhajiroun, an Islamist group founded in 1996.

In the United States, threats include the 18th Street Gang, an Hispanic-based crime syndicate founded in the 1960s, and Mara Savatrucha, a violent Latin-American organisation founded in the 1980s that now has as many as 10,000 members. (Editing by Robert Woodward)

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