Pakistanis burn an effigy of Barack Obama in Lahore: resentment of Nato after the death of 24 soldiers last week has plunged co-operation between the allies into doubt. Photograph: Arif Ali/AFP/Getty Images

Nato commanders are planning a substantial offensive in eastern Afghanistan aimed at insurgent groups based in Pakistan, involving an escalation of aerial attacks on insurgent sanctuaries, and have not ruled out cross-border raids with ground troops.

The aim of the offensive over the next two years is to reduce the threat represented by Pakistan-based groups loyal to insurgent leaders like the Haqqani clan, Mullah Nazir and Hafiz Gul Bahadur. Nato hopes to reduce the level of attacks in the eastern provinces clustered around Kabul to the point where they could be contained by Afghan security forces after transition in 2014.

The move is likely to add to the already tense atmosphere following the recent border post attack by Nato helicopters that killed 24 Pakistani soldiers. On Thursday, Pakistan's army chief, General Ashfaq Kayani, ordered his troops to return fire if they came under attack again by its ally.

While drawing down forces in Helmand and Kandahar, the US will step up its presence in eastern provinces bordering Pakistan, bringing the long-festering issue of insurgent sanctuaries in the Pakistani tribal areas to a head. The message being given to the Pakistani military is that if it cannot or will not eliminate the havens, US forces will attempt the job themselves.

Western officials had been encouraged by the fact that a blitz of drone strikes against commanders loyal to insurgent leaders Jalaluddin and his son Sirajuddin in Miran Shah, the capital of North Waziristan, and against forces loyal to Mullah Nazir in South Waziristan, had produced few civilian casualties and no reaction from the Pakistanis. Consequently, an increase in cross-border raids by special forces – and even the withdrawal of the Pakistani army to create a free-fire zone – have not been excluded.

"The Pakistanis may not have the strength to defeat the Taliban and the Haqqanis on their own, even if they wanted to," a western diplomat said.

It is unclear to what extent the killing of 24 Pakistan soldiers will have on the Nato strategy. An investigation is underway into the incident, which appears to have started with an exchange of fire between Pakistani and mixed Afghan-Nato forces, with the latter calling in air support. Nato sent in aircraft believing the fire from the Pakistani side was from insurgents.

As a consequence, Pakistan has closed supply routes used by the Nato-led International Security Assistance Force (Isaf) and barred the US from using a Pakistani air base to launch drones. However, Nato officers said that Pakistani forces had been co-operative in a similar incident on Tuesday, helping prevent it from escalating.

Isaf statistics published earlier this week showed a 7% drop in insurgent attacks across Afghanistan in the first 10 months of this year compared to the same period last year. The decrease in the Helmand area was 29%. But in the eastern provinces the figures show a 21% rise in attacks, now the most violent area, accounting for 39% of all attacks.

The Isaf commander, General John Allen, said the need to confront the sanctuaries in Pakistan was "one of the reasons we are shifting our operations to the east".

In an interview in Kabul, Allen, a US marine, did not give specifics of the strategy and said nothing about cross-border operations. The day before the fatal border clash, he had met Kayani, to discuss cross-border co-operation ahead of the eastern surge, clearly hoping the move against the sanctuaries would be a joint effort.

Allen said he did not know what the long-term consequences of last Saturday's clash would be, describing it as a "tragedy", but made clear that the push to the east would continue.

"Ultimately the outcome we hope to achieve in the east is a reduction of the insurgent networks to the point where the ANSF [Afghan National Security Forces] can handle them, reducing them in 2012, if necessary going after them in 2013," Allen said.

"I wont go into the specifics of the operations but as we consolidate our holdings in the south and as the population centres there in the Helmand River valley and in [Kandahar], we will conduct substantial operations in the east … the idea being to expand the security zone around Kabul.

"In particular we are going to pay a lot of attention to the south of Kabul – Wardak, Logar, Ghazni, Zabul. Because in the end if you have a population in the south that feels secure and it's secured by the ANSF, and you have a population in the east in and around the centre of the gravity of Kabul, and those two are connected by a road so you have freedom of movement, you have a pretty good outcome."

http://www.guardian.co.uk/world/2011/dec/02/nato-offensive-east-afghanistan-pakistan