Taliban insurgents fighting in Afghanistan and Pakistan have been hit by a wave of defections and betrayals that has resulted in a witch-hunt within the militant movement.

The news has boosted morale among commanders of the Nato operation in Afghanistan, which includes more than 6,000 British soldiers. The British contingent has struggled to contain the insurgency in the country's southern provinces over the past 18 months. Last week saw renewed violence with a series of suicide bombings.

However, two of the Taliban's most senior commanders have now been killed after being betrayed by close associates. Up to a dozen middle-ranking commanders have died in airstrikes or other operations by Afghan, Nato or Pakistani forces based on precise details of their movements received from informers. Few details have been publicly released, but senior military sources speak of 'major hits' that they wish they could talk about openly.

The successes may be the result of the more sophisticated strategy now employed by coalition, Afghan and Pakistani forces, say observers.

'There have been desultory efforts over several years to penetrate the Taliban and to play off the various factions within the militancy and along the frontier against each other, but now that has become the keystone of the intelligence effort,' said one Pakistan-based source. 'That's paying off.'

Last week three Central Asian militants were killed in a Pakistani army operation against makeshift training camps and Nato airstrikes in western Afghanistan are thought to have wiped out a dozen mid-ranking Taliban members returning from a meeting.

'There is a feeling that there are spies everywhere,' said one tribal leader speaking by telephone from the violent and anarchic North Waziristan 'tribal agency' along Pakistan's border with Afghanistan. 'People are very worried and no one is trusting anyone any more.'

One suspected spy in North Waziristan, Saidur Rehman, 50, was shot dead 10 days ago after being tortured. A note pinned to his body accused the victim of 'working for the Americans'.

Taliban sources have confirmed that two men had been arrested for betraying Mullah Dadullah Akhund, a brutal and powerful military commander who was killed earlier this month. 'We have captured the spy who helped US forces kill Mullah Dadullah, said Shahabuddin Atal, a Taliban spokesman speaking by telephone from an undisclosed location.

Atal said Dadullah had stopped at the suspect's house in the Bahramcha district of Afghanistan's Helmand province when he came under attack from coalition forces. Those accused of spying are brutally executed. One suspected traitor accused of betraying senior commander Mullah Akhtar Mohammed Osmani last December was decapitated with a knife by a 12-year-old boy before cameras. Such scenes revolted even some members of the Taliban as well as local tribesmen who try to navigate a careful path between the Pakistani army and government and local Afghan, Central Asian and Arab militants.

However, Hassan Abbas, a retired police chief on the Northwest Frontier and an expert on radical Islam, said that many were unjustly accused of spying. 'A lot of those killed are just local maliks [chiefs] who have had contact with the government,' he said. 'They are not spies.'

According to Taliban sources, Dadullah's body was recovered by his fighters after the airstrike, but further information passed to coalition forces by a spy allowed the corpse, later displayed to the media, to be retrieved. 'Each time there was a [coalition] strike the man would disappear and then reappear after the bombing was over,' Atal said. 'He has now confessed.'

The Afghan national intelligence department in Kabul said that Dadullah had been tracked 'with [the] most modern intelligence technology from the Pakistani border before being killed'.

Three Taliban prisoners, among five senior militant commanders controversially freed early this year in return for the release of a kidnapped Italian journalist, died alongside Dadullah, Afghanistan security officials said.

The continual attrition of high-level commanders has hindered efforts by the Taliban to launch a major 'spring offensive'. However, it has successfully maintained a relatively high rate of suicide bombings and similar attacks and has maintained its hold over large portions of southern and southeastern Afghanistan.

According to Rahimullah Yusufzai, a senior Pakistani journalist and expert on the Taliban, 'suspicion is now falling even on trusted men and is creating tension in Taliban ranks'.

Dadullah Mansoor, brother and replacement of Mullah Dadullah, on Friday pledged to continue fighting the 'Western occupation' of Afghanistan.