PESHAWAR, Pakistan (AFP) - Overland oil supplies to Nato troops in Afghanistan resumed through Pakistan on Wednesday with stepped up security after a four-month hiatus due to attacks, Pakistani officials said.

Pakistani contractors stopped driving oil supplies from Karachi on the Arabian Sea to the Torkham crossing on the Afghan border in June due to frequent attacks on their vehicles.

"We resumed these supplies from today after hiring the services of a private firm, which will provide security to our convoys from Karachi to Torkham," contractor Azad Khan Afridi said.

He said contractors suspended supplies after the government refused to provide them with extra security.

Four oil tankers had now reached the border town and were undergoing security clearance, Afridi said.

Paramilitary Frontier Corps troops also escorted the tankers to the border.

A local administration official, Miraj Khan, and a local intelligence official also confirmed resumption of supplies.

Pakistan is a key transit route for the Nato mission in landlocked Afghanistan.

From November 2011 to July 2012, Pakistan shut its Afghan border to all overland Nato traffic after botched US air raids killed 24 Pakistani troops.

Pakistan and the United States have signed a deal allowing Nato convoys to travel into Afghanistan until the end of 2015.