Wednesday's insurgents sent text messages to contacts in Pakistan before launching an attack on three government offices that left 28 people dead, Afghanistan's intelligence chief told reporters. Previous high-profile attacks in the capital have also been blamed on militants based in Pakistan.
In recent months, however, the US and Pakistani militaries have begun cooperating to try to secure the border by sharing intelligence and coordinating offensives on either side of it.
"We've gone from almost a stalemate situation in the mountains to gaining an advantage we didn't have before," says Col. John Spiszer, the commander of US forces in the northeastern border areas.
For years, Afghan and Western officials have complained that the lack of coordination with Pakistan was undermining the war effort in Afghanistan. The problem became so grave in US eyes that President Obama appointed veteran diplomat Richard Holbrooke as special representative to both nations. He arrived in Kabul Thursday from Pakistan as part of a regional tour.
Afghan insurgents fighting near the border often cross into Pakistan when under US military pressure; Pakistani militants filter into Afghanistan to join the insurgency there. For years, weapons and insurgents have been able to slip through mountain defiles along the border with little difficulty.
"The US needs Pakistan to help block the border," says Haroun Mir with the Kabul-based Afghan Center for Research and Policy Studies. "The initial signs say that the cooperation is working, but we should wait and see how it goes over the long term."
"Without Pakistan's military cooperation," he adds, "it will be impossible to win this war."
While American and Pakistani military officials began sharing information in 2007, only in the fall of 2008 did the militaries start collaborating on a closer level.
The rise of a common enemy – Taliban-linked insurgents are at war with the Afghan and Pakistani governments – pushed the two militaries to closer cooperation, analysts say. For example, TNSM, an extremist group led by Maulana Fazlullah in control of Pakistan's Swat district, is also very active in the Afghan border provinces, according to US intelligence officers.
The cornerstone of the US and Pakistan's new joint effort is a US military campaign launched last fall in the Afghan border region dubbed Operation Lionheart, which seeks to complement Pakistani military offensives in the Pakistani tribal districts of Bajaur and Mohmand.
The militaries coordinate their movements so that insurgent escape routes are cut off: Pakistan's role is to block Afghan insurgents from fleeing into Bajaur, and US forces are to stop Pakistanis from escaping into the neighboring Afghan province of Kunar.
When US commanders receive word that the Pakistani Army is operating in a particular area, they send troops to the Afghan side of the border, Colonel Spiszer explains. "At this point, this means [sending] a four-vehicle patrol, but it's better than nothing."
US forces also communicate often with their counterparts across the border, and field commanders on both sides meet to exchange information and discuss tactics.
Commanders are also reinforcing troop strength along the border. A new US battalion recently arrived in Kunar, part of a likely escalation of US forces here.
Over the past year, US forces helped initiate a recruiting drive for the Afghan Border Police (ABP). In Afghan provinces near Bajaur, the ranks of the ABP have almost tripled, according to US military officials.
While the winter months usually see a lull in fighting in Afghanistan, as guerrillas head to warmer climes in Pakistan, the tightened border may be keeping more fighters in the country. Insurgent-initiated attacks in Kunar more than doubled in January compared with the same period last year, says Sami Kovanen, a security analyst in Kabul.
In addition, most of the attacks failed to kill US troops, who have low casualty rates in Kunar despite the high levels of violence there. Spiszer suggests that guerrillas may be having a harder time bringing casualty-inducing heavy artillery into the country.
At the same time, tensions still exist between the allies. The CIA and Special Forces – which operate outside the US military command that is cooperating with Pakistani forces – have repeatedly fired missiles into Pakistani territory, an issue that inflames lawmakers and locals there.
Some US officials say Pakistan covertly supports certain militant groups that are active in Afghanistan. These groups are not at war with Islamabad and instead reserve their fire for American troops. Such groups include the Haqqani network, which has a strong presence in southeastern Afghanistan, and Lashkar-e-Taiba (blamed by India for the Mumbai attacks), which is very active in Kunar.
Military officials say that such tensions are primarily political and don't affect combat operations.
Longstanding frictions also exist between Kabul and Islamabad. But officials say that the greater military cooperation on the border has brought the Afghan and Pakistani militaries closer together as well.
"Whereas the Afghan border police and the Pakistani [forces] once had significant disagreements, they are now sitting down and having tea together," says Capt. Benjamin Brink, an officer involved in coordinating border activities. "They realized over the last year that there is a common foe."