By Ahmad Sultan

TORKHAM, Pakistan (Reuters) - Pakistani and Afghan soldiers clashed overnight at the main border crossing at the end of the Khyber Pass, officials said on Monday, with at least one killed and several wounded, further straining relations between the militancy-plagued neighbors.

One Afghan soldier was killed and six were wounded, an Afghan official said. The Pakistani army said one of its soldiers was wounded in the fighting at the Torkham Gate crossing in the mountainous region of northwestern Pakistan and eastern Afghanistan.

Both countries blamed each other for starting the fighting, which broke out at roughly 9 p.m. local time on Sunday and continued into the night.

"We currently have agreed on a ceasefire with #Pakistan. We hope this problem will end through the work by diplomatic addresses," the Afghan government's chief executive, Abdullah Abdullah, said on Twitter.

"The current fight Pakistan started doesn't help anyone's interest."

Relations between the neighbors have been strained in recent months. Kabul has accused Pakistan of harboring militants seeking to topple the Afghan government, including the notorious Haqqani network, blamed for high-profile attacks in the capital.

Pakistan denies supporting militants and said it was constructing a border gate near Torkham, a Pakistani town close to the frontier, to prevent militants crossing from Afghanistan into Pakistan.

"In order to check movement of terrorists through Torkham, Pakistan is constructing a gate on its own side of the border as a necessity to check unwanted and illegal movement," Pakistan's army said in a statement.

"Pakistani security forces responded to Afghan firing effectively."

Ayub Hussainkhil, border police commander in eastern Afghanistan, said the fighting at the Torkham Gate stopped at t 5 a.m. on Monday.

"We have received reinforcement and are ready to defend our country until the last drop of blood in our bodies," he said.

The Pakistan-Afghanistan border has long remained porous and disputed. Afghanistan has blocked repeated attempts by Pakistan to build a fence on sections of the roughly 2,200-km (1,370-mile) long frontier, rejecting the contours of the boundary.

Last month, Pakistan build a border post between Pakistan's South Waziristan and Afghanistan's Paktika province and handed it over to Afghan officials.

Hours later, Afghan authorities shut the post, saying that the actual border lay about a kilometer inside Pakistani territory.

(Additional reporting by Rafiq Sherzad at TORKHAM. Asad Hashim in ISLAMABAD; Writing by Drazen Jorgic; Editing by Nick Macfie)