"Pakistan has strongly protested with Afghanistan on the cross-border attacks and I will also take up this issue with Karzai," Ashraf told reporters in Karachi.
His office did not elaborate on when such a conversation might take place.
Pakistani officials said militants killed six troops on patrol in the Soni Darr area of Upper Dir, a northwestern Pakistani district on the Afghan border.
Intelligence officials said the attackers were loyalists of Maulana Fazlullah, who fled into Afghanistan when the army recaptured the Swat valley after a two-year Taliban insurgency ended in 2009.
Afghanistan and Pakistan trade accusations of blame for Taliban violence plaguing both sides of their porous, mountainous border.
Pakistan says rebels have regrouped in eastern Afghanistan. Afghan and US officials want Pakistan to eliminate Taliban and al Qaeda-linked havens used to launch attacks in Afghanistan.
Pakistani troops have been bogged down for years fighting local Taliban but have resisted US pressure to carry out a sweeping offensive against Afghan Taliban fighters in its North Waziristan district.
US Defense Secretary Leon Panetta warned Islamabad earlier this month that Washington was running out of patience over terror safe havens.
Islamabad imposed a blockade, now in its seventh month, on overland NATO supplies into Afghanistan since US air strikes killed 24 Pakistani soldiers along the Afghan border on November 26.
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There's a difference between an attack by insurgents and by military. The six Pakistani soldiers were killed during a cross border attack from Afghanistan, but the perpetrators were not the Afghan military but loyalists of Maulana Fazlullah, leader of theTehreek-e-Nafaz-e-Shariat-e-Mohammadi (TNSM), a banned Pakistani Islamic fundamentalist militant group allied to the Pakistani Taliban, who have found shelter in Afghanistan.
Pot calling the kettle black.