Pakistan was plunged into darkness after a key power transmission line broke down early on Sunday in an incident blamed on a rebel attack, the latest reminder of the country's crippling energy crisis.

The power failure, one of the worst Pakistan has experienced, caused electricity to be cut in major cities throughout the country, including the capital Islamabad.

It was later restored in much of the country, with the national power company saying normal distribution would resume within hours.

Officials said the blackout began after midnight when a transmission line connecting a privately-run power plant to the national grid was damaged.

A senior official at the National Grid station in Islamabad said around 80 percent of the country was hit by power breakdown.

An AFP reporter in the eastern city of Lahore said the airport was also affected by the breakdown.

Minister of State for Water and Power Abid Sher Ali later issued an apology and said electricity had been restored in most of the country, blaming the breakdown on rebels blowing up the line in Naseerabad district, which lies in southwestern Baluchistan province.

A spokesman for the national power company said that "electricity has been restored in all parts of the country."

"Some 6,000 megawatts of electricity has been added to the national system and within a couple of hours distribution will be normal," the spokesman said.

Pakistan's electricity distribution system is a complex -- and delicate -- web and a major fault at one section often leads to chain reactions and breakdowns of power generation and transmission.

In addition to chronic infrastructure problems, the energy sector is also trapped into a vicious "circular debt" brought on by the dual effect of the government setting low electricity prices and customers failing to pay for it.

State utilities therefore lose money, and cannot pay private power generating companies, which in turn cannot pay the oil and gas suppliers, who cut off the supply.

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Earlier this week, Prime Minister Nawaz Sharif cancelled his trip to the World Economic Forum in Davos to deal with a severe petrol shortage at home.

The fuel crisis began last week when Pakistan State Oil was forced to slash imports because banks refused to extend any more credit to the government-owned company, which supplies 80 percent of the country's oil.

Solving Pakistan's energy crisis was a key campaign pledge for Sharif in the run-up to the 2013 general election, and the shortage is heaping fresh pressure on his government.