A new bout of fighting erupted on Monday in a border area between Afghanistan and Pakistan, the latest indication of a sharp deterioration in relations between the important U.S. allies.
Pakistan is seen as vital in bringing stability to Afghanistan as most Western forces prepare to withdraw by the end of next year.
The United States and other powers involved in Afghanistan have been trying to promote cooperation between the Asian neighbors, who have a history of mistrust.
Afghan officials said the clash on Monday erupted after Pakistani troops tried to repair a gate on the border, in the Afghan district of Goshta, where last week an Afghan border policeman was killed in an exchange of fire.
It is unclear if there were any casualties on Monday.
"This morning's clash began after the Pakistani side continued to repair the gate, which was damaged in the previous fighting," said Ahmad Zia Abdulzai, a spokesman for the governor of Nangarhar province.
Afghanistan says the gate at Pakistan's Gursal military post encroaches on its territory. The Nangarhar governor has spoken several times to Pakistani consular officials to tell them not to repair the gate, Abdulzai said.
Pakistani military spokesmen were not immediately available for comment.
Afghanistan and Pakistan have had testy relations since Pakistan was formed in 1947, at the end of British colonial rule over India. Afghanistan has never officially accepted the border between them.
Pakistan helped the Taliban take power in Afghanistan in the 1990s. Many Afghan leaders say Pakistan is still helping the militants, seeing them as a tool to counter the influence of its old rival, India, in Afghanistan.
Pakistan denies helping the Taliban and says it wants peace and stability in its western neighbor.
But in an indication of how bad ties have become, Afghan President Hamid Karzai, without naming Pakistan, last week called on the Taliban to fight Afghanistan's neighbor, where, he said, plots were made against Afghanistan.
Earlier last week, troops from the two sides exchanged fire for about five hours.
Karzai has ordered officials to take "immediate action" to remove the gate and other Pakistani military installations near the Durand Line, the 1893 British-mandated border.
Afghanistan maintains that activity by either side along the Durand Line must be approved by both countries.
(Reporting by Rafiq Sherzad; Writing by Dylan Welch; Editing by Robert Birsel)