KHOST, Afghanistan (Reuters) - Afghans call them 'night letters' -- notes scattered or pushed under doorways by Taliban militants in the dead of night, threatening villagers' lives if they cooperate with foreign forces and the government.

The threats have picked up in recent weeks in areas across southeastern Afghanistan, U.S. officers and Afghans say, as the Taliban intensify their activities along the Pakistan border and in mountainous communities inland towards Kabul.

The notes are often poorly written but the message is clear -- have nothing to do with the foreign troops or serve in the government they back, otherwise, your business will be destroyed, your livestock snatched or your throat cut.

At least six people have had either throats slit or were beheaded by the militants for allegedly acting as spies for the foreign forces only in recent weeks in various parts of southeastern Afghanistan, according to officials and the Taliban.

Scores have lost their lives for failing to take notice of the Taliban's verbal threats, or in the form of the 'night letters', since 2006 when the al Qaeda-backed Taliban made a return.

"It's usually the merchants or those with something to lose," says Lieutenant Augie Gonzalez, a platoon commander based at a camp outside Khost, a city in the southeast of the country, 20 km (13 miles) from the Pakistan border.

"The threats are for real and it gets to them, you sense it," he says, explaining how he'll often visit a village to talk to local leaders and deliver food and other aid, only to return three days later and learn the Taliban have been there.

"The villagers don't want the Taliban there, there's no sympathy and they'll tell you that straight, but they can't take them on their own and we can't be there every day."

The night letters form part of a campaign of intimidation and violence that appears to be steadily escalating, although the commander of U.S. forces in the area, Colonel Pete Johnson, dismisses suggestions of a renewed Taliban offensive.

Four U.S. troops and a U.S. civilian were killed in ambushes or roadside bomb attacks last week alone, while Afghan security forces, particularly the less well organized police, have also repeatedly been targeted, with around a dozen killed.

"Yes, there's more fighting right now than there was last month, but that's just the way the context is in eastern Afghanistan," Johnson told Reuters last week, describing the idea of a Taliban offensive as a "myth."

Lieutenant Gonzalez and his men don't see their day-to-day work as countering a Taliban offensive. Instead it's more about trying to get into villages and win the population over before the militants have a chance to do so and impose their will.

"It's a slow process of pushing forwards, providing security so that others can come in and rebuild," says Gonzalez.

Yet, the Taliban threat is very real -- a roadside bomb that killed two U.S. soldiers last week also left two severely wounded: both had their legs amputated and both may lose an arm.

A soldier in the same platoon, traveling three vehicles behind the one that was hit, has survived six roadside bomb attacks already and he's only been in Afghanistan six weeks.

"It's been pretty intense," said the soldier, Private Mullan, clearly shaken and not wanting to give his full name. "Sometimes we've had a series of events that have gradually built up, other times it's been quieter."

For Afghans, the Taliban threat is very real and there is no doubt in their minds it has risen in the past month as the season has shifted and it's become easier for militants to move across the border from Pakistan into Afghanistan.

Saif, a translator working with the Americans who lives in a remote district outside Khost, says night letters are commonplace and threats have been carried out. Schools have been burnt down and district centers, the focal point for local rebuilding and development, attacked and destroyed.

He is quick to emphasize, though, how "little" sympathy there is for the Taliban in his area, where most regard them as "poorly educated thugs with little proper religious grounding."

He recounts how some members of the Taliban were recently captured following a botched attack. One was a simple young man who was asked by his captors to show them how to pray. "He didn't know how," the translator said. "He couldn't even start."

Ousted from power in 2001 for sheltering al Qaeda leaders, the Taliban have vowed to drive out the foreign troops from Afghanistan and topple the central government.

In their campaign, the Taliban also target any one working or helping the government or the foreign forces.