Islamabad, Pakistan (CNN) -- Attackers in Pakistan have hit another convoy carrying fuel for NATO troops in Afghanistan, killing one person, authorities said.

The attack, which occurred Monday, was the fourth attack in as many days on convoys carrying fuel to support the NATO forces.

Gunmen fired on a convoy of oil tankers in the Kalat district of Pakistan's western Balochistan province, said Bashir Ahmed, a police official in Kalat. One person died, police said.

Attackers struck two convoys on Friday and a third on Sunday.

The Pakistani Taliban has claimed responsibility for two of those attacks, a central spokesman for the militant group told CNN by telephone Monday.

One of the attacks took place Friday against a convoy of NATO supplies near Shikarpur in the southern Sindh province. The other took place Sunday in the capital of Islamabad, killing three local guards.

Azam Tariq, the Pakistani Taliban spokesman, said both the recent attacks on NATO supply efforts were carried out as revenge for drone strikes and NATO's attacks in Pakistan.

"U.S. and NATO forces are killing innocent Pakistanis, which is unacceptable, and we will teach them a lesson by such attacks," Tariq said.

On Monday, Islamabad police said four people were arrested in connection with the Sunday attack, which also left eight drivers injured.

A convoy was attacked in Baluchistan on Friday, killing a driver and his aide. The Taliban has not claimed responsibility for that attack.

The convoys are operated by contracting Pakistani logistics firms, using local trucks and drivers.

The Pakistani Taliban said a special squad has been appointed to hit U.S. interests in Pakistan, especially NATO supply efforts.

"The special squad is fully capable to cut off the route for NATO supplies by carrying attacks on the trucks," Tariq said.

"I give final warning to the drivers and the owners of the trucks to stop working for NATO, otherwise our squad will make them exemplary," Tariq said.

Pakistan halted NATO supply convoys from entering Afghanistan Thursday after officials blamed cross-border NATO helicopter fire for the deaths of three Pakistani soldiers.

The troops were killed when three NATO helicopters crossed from Afghanistan into Pakistani airspace early Thursday and attacked a military outpost, the government said.

On Monday, NATO's secretary general said an investigation has been launched into the incident.

"I expressed my regret for the incident last week in which Pakistani soldiers lost their lives, and my condolences to the families. Obviously, it was unintended. Obviously, we have to make sure we improve coordination between our militaries and our Pakistani partners," NATO Secretary General Anders Fogh Rasmussen said.

Pentagon spokesman Geoff Morrell said he expects findings of a NATO probe into the Pakistan incident to be released Wednesday night.

Morrell also said the U.S. military is hopeful that the closed supply route from Pakistan to Afghanistan will be opened "as soon as possible," but the closure has not affected the ability to supply NATO troops.

"We are making progress on that front," Morrell said at a news conference on Tuesday, in reference to talking to Pakistan's government about reopening the Torkham gate.

Morrell said that the fuel convoy attacks by the Taliban have affected about 1 percent of the supplies that move from Pakistan to Afghanistan.

The route is most important for fuel transport but said even if the gate remained closed for a while, the ability to supply fuel to troops in Afghanistan would not be affected, he said.

Journalists Nasir Habib, Nasir Dawar and Laura Perez Maestro contributed to this report.