LONDON 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 Guardian reported on Friday. The aim of the offensive over the next two years is to reduce the threat represented by allegedly Pakistan-based groups loyal to insurgent leaders like the Haqqani clan, Mullah Nazir and Hafiz Gul Bahadur. 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. 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 Army Chief Gen Ashfaq Kayani ordered his troops to return fire if they came under attack again by its ally. Meanwhil0e, according to a private TV channel, Pentagon has said that Pakistan will not be part of the probe into the border attack. INP adds: The US has said it was in early stages of investigation into the cross-border Nato raid that killed 24 Pakistani soldiers and was not apologising to Islamabad, as of now. We need to find the results of this investigation. We have offered our condolences. I am not going to prejudge about that action we might take in the future, White House press secretary, Jay Carney said. when specifically asked if the White House has decided that US President Barack Obama would not apologise for the incident, as was reported by The New York Times. Carney termed it as 'utter nonsense when asked if this decision of the Obama Administration was based on political considerations. He said the White House, he himself and other members of the government have already expressed their condolences on the death of Pakistani soldiers. There was a suggestion from the US Embassy in Pakistan about taping a message of condolences, Carney said.