In the latest raid on Wednesday, two rockets were found and 16 men were arrested about 15km north of Kabul. They were suspected of plotting to smuggle weapons into the heavily guarded capital, international peacekeepers said. 

"Certainly we have seen an increase in the number of people being detained, weapons caches found, here in the city," said Commander Chris Henderson, a spokesman for NATO-led peacekeepers who took part in the raids. 

Kabul, where 6500 NATO-led international peacekeepers are concentrated, has been relatively free of large-scale violence since late January when a British soldier was killed and three were wounded in a human bombing. 

But NATO's commander in Afghanistan, Lieutenant General Rick Hillier, said this week the armed fighters have opened a new front in Kabul after launching a spring offensive in the south and east. Many of those arrested had specific city targets, he said. 

Controversial airstrip

The US military has announced that a new airstrip has been built in Paktika province near the Pakistan border "to re-position forces quickly throughout the region" and assist in the hunt by 15,500 US-led foreign troops for al-Qaida and Taliban fighters. 

"The US military buildup in Paktika is a matter of concern not only for Pakistan and Afghanistan but also for other countries of the region"

Hafiz Husayn Ahmad,
Leader of the Islamist alliance Muttahida Majlis-e-Amal

But Islamist politicians in neighbouring Pakistan said on Wednesday they were "concerned" about it, as one newspaper warned it could precipitate a spillover of US military action into Pakistan. 

"The US military buildup in Paktika is a matter of concern not only for Pakistan and Afghanistan but also for other countries of the region," Hafiz Husayn Ahmad, a leader of the six-party Islamist alliance Muttahida Majlis-e-Amal (MMA), told reporters. 

"The building of an airbase shows the long-term designs and
plans of US in the region," Ahmad said. "Instead of building airbases, the US should now better get out from Afghanistan and Iraq after handing over control to United Nations."