KANDAHAR, Afghanistan - A wave of violence sweeping the southern city of Kandahar has forced the United Nations to tell more than 200 of its Afghan employees to stay home, a UN official said Monday. Several foreign UN employees were temporarily moved to Kabul.

The announcement came hours after three bombings -- one aimed at a top police official -- shook the city and left two civilians dead.

UN spokesman Dan McNorton insisted the world body is not pulling out of Kandahar, but he declined to say how many employees would still work in the troubled city, where NATO is ramping up an operation to rout the Taliban. He would only say "several" non-Afghans had been moved to the country's capital.

Afghans working for the UN and other foreign organizations are frequently targeted by militants as well.

"There is always a balance to be struck to ensure the safety of our staff and ensure that we can deliver our programs and humanitarian assistance to the people of Afghanistan," McNorton said. "We constantly have to adapt our ways of working."

"We will continue to monitor the security situation in Kandahar and hope to be able to get back to work as soon as possible," he added.

The UN has been on the defensive in Afghanistan since last October, when three suicide attackers stormed a Kabul guest house where dozens of staffers lived, killing five UN employees and three Afghans. The three assailants also died during the two-hour siege.

In the wake of that attack, the world body sent about 600 of its 1,100 foreign staffers either out of the country or moved them into more heavily secured quarters. Many eventually were recalled to Kabul; others chose not to renew their contracts or terminated their tours in Afghanistan early.

Two of Monday's blasts -- which occurred within a minute of one another when bombs planted about 10 metres apart exploded in downtown Kandahar -- were aimed at the passing convoy of Deputy Provincial Police Chief Fazel Ahmad Sherzad.

"They were targeting the car I normally use, but luckily I was not in it at the time," Sherzad said.

About two hours later, a third blast struck in the north of the city.

The looming offensive and a surge in militant attacks -- on local officials, aid workers and contractors for U.S. development projects -- has left Kandahar's half-million inhabitants increasingly terrified.

"The security in this city is deteriorating," said Enayutullah Khan, 43, a rickshaw driver. "People leave their homes only to find food for their children. Otherwise we don't leave the house."

Rangina Hamidi, who runs a Kandahar-based handicrafts business that employs about 200 women, said many of her workers had been too frightened to come to work in recent days.

"It's very scary. We don't know what is happening," said Hamidi, whose employees sew embroidered clothing, tablecloths and shawls.

Kandahar is the largest city in southern Afghanistan and the birthplace of the Taliban, which still has considerable support here. A U.S.-led operation planned for this summer aims to clear Kandahar of Taliban fighters and break the grip of warlords who have allowed the fighters to slip back in.

President Barack Obama has ordered 30,000 more troops into Afghanistan, in part to back up the Kandahar offensive. The operation will be a critical test of the Afghan war.

But the Taliban have launched increasingly deadly attacks ahead of the offensive. Since April 12, at least 20 civilians have been killed in Kandahar, including children. Aid workers also have been targeted.

Monday's first two explosions killed two civilians and injured one police officer and one civilian, the Interior Ministry said. Another policeman was injured in the blast in the city's north.