The fierce fighting erupted in the Paktika province in which 25 Afghan soldiers and resistance fighters were killed at the weekend.
The US soldier's death on Thursday from wounds, brings to at least 68 the number of US soldiers killed since the start of the war in Afghanistan on 7 October 2001.
Pakistan has pledged to support Afghanistan's US-backed government after persistent charges it has aided a resurgence of the Taliban.
Speaking after talks in Kabul, Pakistan's Foreign Minister Mian Khursheed Mehmood Kasuri rebuffed accusations that Pakistani troops traversed the Afghan border and promised closer and better cooperation with its war-ravaged neighbour.
The two countries are “tied to each other almost like twins and when one sneezes then the other catches flu,” Kasuri told a press conference.
“We will do everything that we can to support the present government," he added, Reuters reported.
The Afghan government, led by US-installed Hamid Karzai, has charged Pakistan with allowing the Taliban to launch attacks from its border regions and of occupying part of its territory.
Pakistan’s Inter-Services Intelligence, the country’s intelligence security service, was often cited as the main backer of the Taliban before Pakistan joined the US-led War on Terror in 2001.
Kasuri's two-day visit to Afghanistan follows one of the bloodiest weeks in Afghanistan since the Taliban, which sheltered Usama bin Ladin, were ousted in 2001.
Recent skirmishes have claimed the lives of more than 90 people.
Some Afghan politicians blame the attacks on international guerrilla groups with links to al-Qaida. The incidents have largely taken place in the east and southeast of the country.
A bomb, last week, exploded on a passenger bus killed 15 in Helmand province. A further 25 people perished in inter-warlord fighting in Uruzgan.
The increase in violence has resulted in a number of international aid agencies suspending operations, only worsening the plight of the country’s poverty stricken population.
Pakistan is however in a precarious position.
Bin Ladin links
President Musharraf, who came to power in a military coup in 1999, backed the war against the Taliban, buckling under US pressure and succumbing to promises of billions of dollars worth of humanitarian assistance.
This angered many Pakistanis who believed their illegitimate president had signed a Faustian pact.
Members of his own intelligence services have been accused of maintaining close links to both bin Ladin and al-Qaida.