Cross-border clashes flared Monday between Afghan and Pakistani security forces for a second time in five days as Kabul and Islamabad engaged in a war of words over the porous frontier, officials said. On the edge of the Afghan capital, more than 2,000 people, mostly villagers, demonstrated and chanted "Death to Pakistan!" to protest against the fighting. Relations between the fractious neighbours have become increasingly strained despite renewed efforts last month by US Secretary of State John Kerry to get them to work more closely on peace efforts in Afghanistan. Afghanistan and Pakistan are in dispute over a site where Pakistan has tried to construct a gate on what Afghan officials say is Afghan territory. Clashes last Wednesday in the same spot killed an Afghan guard and wounded two Pakistanis. The border is unmarked in places and a key battleground in the fight against Taliban violence plaguing both countries. "Today the Pakistanis returned to the construction site and said they will rebuild the installations," said Afghan interior ministry spokesman, Sediq Sediqqi. "Our border police told them not to do so. The Pakistanis fired at them and our police returned fire. The fighting lasted for two hours before the Pakistanis requested a ceasefire," the spokesman added. He told AFP the clashes had since stopped and the Pakistani border guards had left the site of the construction. Pakistani officials blamed Afghans for starting the clashes. "Afghan troops opened unprovoked fire from across the border at our post... They fired mortars and automatic weapons," one Pakistan official told AFP on condition of anonymity. "Our troops responded with retaliatory fire. There have not been reports of any casualties so far. The exchange of fire continues at intervals," a second official said, also on condition of anonymity. Afghanistan and Pakistan are both US allies in its battle against militants. But Kabul accuses Islamabad of playing a double game in supporting Taliban insurgent attacks on US and Afghan troops. Pakistan denies the allegations and is locked in its own battle against the Pakistani Taliban. On Saturday Afghan President Hamid Karzai said the cross-border clashes could be an attempt by Islamabad to put pressure on Kabul to accept the "Durand Line", the disputed border which Afghans do not accept. Pakistan's foreign ministry dismissed Karzai's remarks and said "opening discussions on this issue" was a "distraction from the more pressing issues requiring the priority attention and cooperation of Pakistan and Afghanistan". It said Pakistan's post had come under attack and complained about "several threatening and provocative statements" from the Afghan leadership. Pakistan, which backed Afghanistan's 1996-2001 Taliban regime, is seen by the West as having a central role in negotiating a political settlement with Taliban insurgents who shelter in Pakistan's border districts.