A violent Islamist sect responsible for scores of killings in northeast Nigeria is increasingly linking up with global jihadist movements like al Qaeda, a military commander in the area told Reuters Thursday.

Lieutenant Colonel Hassan Mohammed, a senior military official in the Joint Military Task Force (JTF), was speaking at a government house at the end of dusty track in Maiduguri, the heartland of the Boko Haram insurgency.

Boko Haram is al Qaeda, said Mohammed, standing in front of his army truck, dressed in camouflage and flanked by armed soldiers.

I see perfect links. It cuts across boundaries. Al Qaeda has no boundary, Boko Haram has no boundary. All terrorists, one problem.

Many analysts and Nigerians doubt the extent to which Boko Haram has global ambitions -- the group's avowed aim is to introduce sharia law across Nigeria -- but it seems to be growing in sophistication and it is thought they have made contact with al Qaeda's north African affiliate.

They are a growing headache for President Goodluck Jonathan, who Thursday tried to assure investors at an economic summit in the capital the insecurity would be short lived.

Anybody who doesn't want to come and invest in Nigeria now because of these incidents of Boko Haram will really regret it because this is very temporary, he said.

This terrorism is new and we are acquiring the relevant infrastructure to combat it and I assure you that (we) will.

The sect claimed responsibility for multiple gun and bomb attacks that killed 65 people in and around the city of Damaturu Friday in its deadliest attack yet, which left bodies littering the streets.

The attacks followed multiple bomb blasts earlier the same day in nearby Maiduguri, including a triple suicide bombing of a military headquarters, according to the military.

Mohammed said he had unconfirmed reports the two suicide bombers were trained in Afghanistan.

POROUS BORDERS

Nigeria's remote northeast, on the threshold of the rocky Sahel, borders several other African countries, including Cameroon, Chad and Niger, the latter having its own problems with the Sahara-based al Qaeda in the Islamic Magreb.

Mohammed suggested these porous borders were making it easy for militants on either side to move in and out of Maiduguri, a rubble-strewn city of boarded-up shops and soldiers gripping Ak-47s nervously behind sandbagged sniper positions.

The city suffers frequent shootings and bombings usually targeting religious and authority figures or police.

Maiduguri has been a harbour for people from Chad, from Niger, from Cameroon. Now ... the people they have invited have now become a source of terror, he said, agitatedly, declining to sit down during the whole interview.

Nigeria's police said Tuesday they had arrested some suspected militants behind Friday's violence, and last week were searching door-to-door for weapons.

I can tell you many people have been co-operating with us and we have collected many arms, Mohammed said, as two soldiers kept guard. Maiduguri is no longer a safe haven.

Efforts to fight Boko Haram have yielded little so far, and heavy-handed police tactics have radicalised youths, locals say.

I must admit that sometimes men exhibit some excesses, but ... We have handed over people to the police who will be prosecuted, Mohammed said.

But residents of remote Maiduguri interviewed by Reuters on Thursday saw things differently. Many reported being as almost as scared of the military as they were of the insurgents.

We are afraid -- afraid of bombs but we're also of the JTF, said Gani Musa, 30, a bicycle mechanic who witnessed a bomb blast opposite his shop in July.

Every time there is a bomb, the military goes berserk, shooting everywhere, he said, grease on his t-shirt from fixing bicycles inside a wooden shack.

In a sign the insurgency has spread beyond the northeast, a bomb attack on the Nigeria headquarters of the United Nations in the capital Abuja in August killed 26 people.

(Writing by Tim Cocks; Editing by Sophie Hares)