While US enemies in Afghanistan and Pakistan are regrouping, the US-backed governments in Kabul and Islamabad are locked in a bitter dispute.
Afghan protesters attacked Pakistan's embassy in Kabul Tuesday and burned the Pakistani flag. The action followed recent claims from President Hamid Karzai that Pakistani forces had "taken" Afghan territory during skirmishes along the lawless and poorly demarcated border.
In response, Pakistan closed its embassy and halted diplomatic relations with Afghanistan.
Analysts say the latest turn of events deals a severe blow not only to the traditional ties between Pakistan and Afghanistan, but to the ongoing US-led war on terror.
"The US wants friendly relations between these two countries to be able to effectively continue joint operations ... to weed out Taliban and Al Qaeda elements," says analyst Jalaluddin Khan. "This standoff will be detrimental to all involved."
US and Afghan forces have been conducting search-and-kill operations in the regions bordering Pakistan to root out remnants of the Taliban, Al Qaeda, and fighters loyal to guerrilla leader Gulbuddin Hekmatyar. On the other side of the border, the US has provided intelligence and communications assistance to Pakistani forces engaged in the same fight.
But with the two US partners at loggerheads, such military coordination may be jeopardized - especially if US forces must divert energies from hunting militants to keeping peace between allies.
The Afghan government said Monday there had been skirmishes along the border in eastern Nangarhar province for several days, some involving military forces from the two countries, some involving tribal militants. Afghan security forces say hundreds of troops have been dispatched to the border.
In April, Afghan and Pakistani border guards briefly battled near the Afghan town of Ghulam Khan in the eastern province of Khost. An erstwhile supporter of the Taliban regime, Pakistan has struggled to develop warmer relations with the new government in Kabul.
The latest dispute between the two neighbors began after Pakistan and US forces conducted joint operations in the Mohmand region of Pakistan and established checkposts along the Durand Line, which forms the border with Afghanistan. Afghan officials accuse Pakistan of an incursion of about 25 miles into their territory. The operation was part of attempts to stop suspected Taliban and Al Qaeda fugitives from carrying out cross-border attacks on Afghanistan.
Pakistan denied the incursion, prompting heated exchanges all the way up to the top of the two governments.
The diplomatic feud boiled over onto the streets Tuesday, as protests over the dispute turned violent.
Some young protesters broke away from a demonstration, climbed the walls of the embassy, and ransacked it. The intruders burned computers and documents and roughed up members of the staff. Many employees hid in the basement.
"The anger was emanating in waves. They broke the glass windows of vehicles and smashed everything in sight," says Mubarak Shah, who witnessed the attack.
The rally was led by the head of the Afghan Bank, Anwar-ul-Haq Ahadi, who exhorted the government to press Pakistan over the incursion into Afghan territory, arguing that otherwise people would be forced to defend themselves and their land.
In a consequent press conference, Pakistan's ambassador to Afghanistan, Rustum Shah Mohmand, lay the blame squarely on the Afghan government for incendiary remarks, saying all diplomatic ties were now at a standstill.
He also linked the attack to President Karzai's statement on Sunday, in which he accused Pakistan of taking territory and interfering with Afghanistan's internal issues.
Ambassador Mohmand said that he had spoken to President Pervez Musharraf, who termed the incident as "sad and unfortunate."
Karzai strongly condemned the embassy attack and apologized to President Musharraf.