KABUL, July 23: Aid workers and Afghan officials are struggling to avert a looming humanitarian crisis as thousands of Afghan refugees living in Pakistan pour across the border.

Over 20,000 refugees have already crossed the border into Afghanistan's insurgency-hit south-eastern provinces, many of them leaving Pakistan after decades with only hours to pack what little they can carry, aid workers said.

"Because of the military operations in South Waziristan many refugees have been forced to leave and because they have no time to pack or gather their things they face difficulties when they come back to Afghanistan," UN refugee worker Paul Stromberg told AFP.

The refugees are streaming into the Taliban stronghold of Paktika province over border crossings where the UN and aid organizations have no presence, said Stromberg, senior repatriation coordinator at the United Nations High Commission for Refugees (UNHCR) in Afghanistan.

Afghanistan's southeastern provinces bordering Pakistan are a hotbed of Taliban-led insurgency. The Afghan government, the UN and most aid organizations have pulled out fearing attacks on their workers.

On the other side of the border, Pakistan is stepping up a five month-long campaign to hunt Al Qaeda-linked fighters in the quasi-independent tribal areas. The government is closing refugee camps believed to be shelters for Mujahideen from Chechnya and Uzbekistan.

The United States has increased pressure on Pakistan to root out Al Qaeda-linked fighters as US presidential elections draw nearer. US Deputy Secretary of State Richard Armitage visited Pakistan a week ago to discuss the "war on terror".

A commission set up to probe the US response to the September 11 attacks also released a report on Thursday calling on the US government to increase its aid to Pakistan as part of a global anti-terror strategy.

"In South Waziristan, there we were taken by surprise, but now we have an idea that there will be more military operations so we are trying to inform the refugees and look for alternatives," Imran Zeb, Pakistani Chief Commissioner for Afghan Refugees, told AFP.

Zeb was part of a Pakistani delegation in Kabul earlier this week to talk with the Afghan government and the UN about how to deal with innocent Afghans caught up in the escalating drive to quash insurgency along the Afghanistan-Pakistan border.

But Afghan officials say low-level trilateral talks on Wednesday between officials responsible for refugees on both sides of the border and the UN are not enough to resolve the issue.

"We have asked President Hamid Karzai to take this issue up on his visit to Pakistan. It would be better if this was discussed at a higher level," Habibullah Qaderi, chief adviser to the Ministry of Refugees and Repatriation, told AFP.