Power supplies to large areas of northern Colombia have been cut off after a series of rebel attacks on the country's electricity pylons.

Officials said up to three million people had been affected by the black-out, and electricity rationing would be introduced while attempts were made to repair the power supply.

Water supplies have also been affected because the plants need electricity to operate.

Conflicting reports blame the Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN) for the attacks.

The Energy and Mines minister, Carlos Caballero Argaez, confirmed the plan to ration electricity.

But he did not say when rationing would be introduced or for how long it would last.

He said: "The rebels must understand that if they destroy power pylons, they adversely affect the entire population."

Knock-on effect

Rebels blacked out swathes of land in Antioquia province, including its capital, Medellin, as well as parts of Choco and Cordoba provinces.

Colombia uses an interconnected power transmission network, so an attack on one part of the system has knock-on effects throughout the country.

The rebels are understood to have attacked at least 17 transmission towers.

One of the most serious attacks was near the town of Guatepe, 51km (35 miles) east of Medellin, at a major power production plant which supplies Antioquia and beyond, the army said.

Electricity has been restored to parts of the blacked out regions. But it is unclear whether the restoration is permanent, or whether there will be further power cuts as repair work is carried out.

Rebel defeat

The FARC rebel group is Colombia's largest rebel group and has recorded a number of successes against the army.

But in recent months the army has hit back, and last weekend military spokesmen said almost 50 guerrillas had died in a battle 50km (30 miles) from the capital, Bogota.

The ELN is a smaller group that has in the past targeted electricity pylons and the country's oil infrastructure