LONDON, Nov 14 (AlertNet) - The U.N. food aid agency has halted relief convoys transporting urgently needed winter supplies into Afghanistan from northwest Pakistan after two looting incidents in the past three weeks.

The temporary suspension could prevent the World Food Programme (WFP) from positioning adequate food stocks in Afghanistan ahead of the winter snows, spokesman Amjad Jamal told AlertNet on Friday.

In late October, Britain's Royal United Services Institute (RUSI) warned that drought and high food prices in Afghanistan had created the conditions for a "calamitous famine". It called on the international community to mount an intensive air operation to deliver life-saving aid similar to the Berlin Airlift 60 years ago.

On Oct. 28, four WFP trucks carrying 208 tonnes of wheat for Afghanistan were looted in Pakistan's Khyber agency by heavily armed attackers. And on Nov. 10, 11 trucks carrying 441 tonnes of wheat were hijacked by Taliban militants as they passed through the Khyber Pass in a convoy with two other vehicles carrying supplies for Western forces in Afghanistan.

Jamal said the agency had a window of only three to four weeks to get enough food into landlocked Afghanistan before winter weather blocks supply routes, but would not start transporting supplies again until local authorities had put in place concrete measures to boost security.

In a third incident on Oct. 21, 263 tonnes of edible oil were set on fire by "miscreants" in Swat district, WFP said. The oil was meant for the agency's school feeding programme in the area and was stored in a facility belonging to the provincial education department.

"The deteriorating security situation in NWFP (North West Frontier Province) is hampering WFP's ability to provide much needed food assistance for the poor in Pakistan and Afghanistan," WFP country director Wolfgang Herbinger said in a statement.

"We are very concerned that people who are already hard hit by food shortages and rising prices are additionally deprived due to such incidents."

Aid agency CARE International warned on Friday that the humanitarian situation in Afghanistan is likely to worsen as winter approaches and dangerous conditions hamstring efforts to combat food shortages caused by drought.

"We are entering a critical time of year," Lex Kassenberg, CARE's Afghanistan country director, said in a statement. "Greater assistance depends on greater security. Without both, more Afghans are going to suffer."

Intensified fighting along the Pakistani border has made matters worse, forcing around 190,000 people from their homes in Pakistan's Bajaur tribal agency and sending around 20,000 refugees into Afghanistan.

And in recent days foreigners have been targeted in a series of attacks in the northwest Pakistani city of Peshawar, including a U.S. aid worker who was gunned down on Wednesday.

Spiralling violence has raised fears that the country could slide into chaos unless its seven-month-old civilian government - also faced with a potentially crippling economic crisis - and the army stem the militant threat.

The U.N. food aid agency has sent a letter to the NWFP government requesting an increase in the local police who regularly accompany its convoys but have been outnumbered by militants in the recent attacks. Soldiers from the army's Frontier Corps could also be used to protect the relief pipeline, Jamal said.

"Also we are trying to do some advocacy that actually the food is meant for humanitarian purposes - that it should not be linked with the NATO supplies or anything else to do with the army," Jamal told AlertNet.

Until October, WFP operations in northwest Pakistan had not come under attack. The agency now fears that the recent upsurge in violence could harm its efforts to help half a million impoverished Pakistani families struggling to feed themselves amid food price inflation.

"Increasing incidents definitely concern us, because food in NWFP is very scarce," said Jamal. "Especially those who have been hit hard by rising food prices, they are suffering already and with these incidents, they will suffer more."

While beefing up security for aid convoys could help get essential supplies into Afghanistan in the short term, there is a need to tackle the political grievances underlying the violence, Jamal said.

"The government must look into those possibilities - what are the worries of these people, why are they increasing violence, what are the root causes of that - and try to mitigate those root causes," he said.

UPDATE: A senior official told Reuters that Pakistan would reopen a main supply route to Western forces in Afghanistan on Nov. 17 and that truck convoys would be given armed escorts. WFP confirmed to AlertNet on Tuesday (Nov. 18) that its transportation of aid across the border into Afghanistan had restarted.

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