Pakistan said on Monday that Afghan and US-led forces had failed to hunt down a Taliban cleric responsible for a spate of cross-border raids despite repeated requests from Islamabad, a complaint likely to deepen tension between the neighbours.
The attacks in which militants loyal to Maulvi Fazlullah took part killed about 100 members of Pakistan's security forces, angering the army which faces threats from multiple militant groups.
"The problem refuses to go away," Pakistani army spokesman, Major-General Athar Abbas, told Reuters.
Fazlullah was the Pakistani Taliban leader in Swat Valley, about 100 miles (160 km) northwest of Islamabad, before a 2009 army offensive forced him to flee.
Also known as FM Mullah for his fiery radio broadcasts, he regrouped in Afghanistan and established strongholds, and poses a threat to Pakistan once again, said Abbas.
Fazlullah, a leading figure in the Pakistani Taliban insurgency, is based in Kunar and Nuristan provinces in Afghanistan, said Abbas.
He is a prime example of the classic problem faced by Pakistan's military. Militant leaders can simply melt away in the rugged mountainous frontier area in the face of army offensives.
In Kabul, National Directorate of Security spokesman Lutfullah Mashal said "terrorist groups usually come from the other side of the border and do some attacks".
"One thing for sure I can say that no one is regrouped or settled here in Afghanistan," he added.
Ties between Kabul and Islamabad, marred by mistrust in the best of times, have been heavily strained in recent months.
First, Afghanistan complained that Pakistan was shelling Afghan border areas in response to militant raids.
More recently, Afghan officials accused Pakistan's spy agency of involvement in the suicide bombing assassination of the chief Afghan peace envoy with the Taliban. Pakistan denied the accusation.
"With this new element, friction will increase. The problem is the issue is highly politicised given the state of affairs in the region, with accusations coming from both sides," said Muhammad Amir Rana, director of the Pak Institute of Peace Studies.
"What was simply a border security issue is now politicised, and will impact bilateral relations."
Fazlullah, who Swat residents said ordered beheadings, public executions and the bombing of girls' schools, is the last thing Pakistan needs.
It is battling a Taliban insurgency, and has been facing stepped up U.S. pressure to attack Afghan militant groups who cross the border to attack Western forces in Afghanistan since U.S. special forces in May killed Osama bin Laden in a Pakistani town, where he had apparently been living for years.
"Now Fazlullah and his group are trying to re-enter Swat through Dir," said Abbas, referring to a border region in northwest Pakistan which was relatively stable before the cleric's men recently staged attacks there on security forces.
The United States wants Pakistan to help stabilise the unruly, mountainous border region once described by President Barack Obama as the most dangerous place in the world.
Doing so would require Pakistan to break up complicated and powerful networks that include al Qaeda, the Afghan and Pakistan Taliban and Arab fighters.
Critics say Pakistan has created chaos in the area by using militants as proxies in Afghanistan to block the influence of old rival India, allegations it denies.
Pakistani officials have urged the United States to focus on defeating its enemies in Afghanistan instead of blaming Islamabad for its failures.
Asked about Pakistan's complaint about Fazlullah, Lieutenant Colonel Jimmie Cummings, a spokesman for NATO's International Security Assistance Force in Afghanistan, said:
"We are working with Pakistan to achieve our shared goals of lasting stability and security in Afghanistan and the broader region."
Residents of the Swat Valley, once a tourist destination with cascading rivers and forest-clad slopes, are still haunted by memories of a life of fear under Fazlullah.
The Taliban capitalised on a widely criticised government peace deal with the Taliban to take control of Swat, home to more than a million people. In April 2009, the United States termed the agreement an abdication to the Taliban.
"There is no village in Swat where Fazlullah's men did not murder someone's brother or father or son. There is no place where they did not destroy homes and families. Most people of Swat are against the Taliban," said Nisar Khan, a 40-year-old farmer in Swat.
"We are now armed, we have weapon permits from the army. There are many soldiers here."