"Al Jazeera understands that there was a specific threat against the UN in Kandahar.
"That at a local mosque near the UN headquarters in the city the Taliban went to the local cleric there and told him to warn residents living around the UN headquarters that they should leave their homes because there was about to be an attack on the UN."
Bays said that when the UN and Afghan forces learned of the threat, they reduced the number of their international staff in Kandahar.
The UN maintained about 40 international staff in Kandahar about a year ago. Now the number is fewer than 10, all of whom have currently been withdrawn.
Our correspondent said the withdrawal of the UN staff is under review. But he said that their return to the office is unlikely until after a planned offensive by Nato forces in June to take control of the area around the city.
However, Ahmad Wali Karzai, a top Afghan official in Kandahar province and the half brother of Hamid Karzai, the president, played down the threat to the UN and said the UN was over-reacting by withdrawing its staff.
Karzai said that the security situation in Kandahar was far worse a few years ago, and he urged the international aid community not to scale back operations in the city.
"We strongly condemn this act by the UN to pull out of Kandahar," he said.
"This is an irrational decision [done] without consulting with local authorities.
"The situation is not as bad as the UN views it. They aren't here for a party. They know they are in a war zone. This move will leave a bad impression on citizens of Kandahar."
New Taliban strategy
But Khalid Pashtoon, an Afghan member of parliament, told Al Jazeera: "In Kandahar the situation has been deteriorating for the last few weeks due to the forthcoming Nato operation.
"The Taliban is starting a new strategy. They are concentrating more in the city of Kandahar, terrorising tribal elders or government officials.
"For the last two or three few weeks, more than a dozen important people have been terrorised in Kandahar."
Pashtoon said that the Nato offensive must go ahead, although there have been concerns that support must first be secured with local tribal leaders.
"If they don't conduct the operation, the situation will become even worse because this will be like a defeat to the interntional community."