By Elliott Gotkine BBC correspondent in La Paz

Bolivia's main opposition leader Evo Morales has told a Bolivian radio station that the government has until Sunday to change its economic policies and nationalise the country's gas resources, or face nationwide blockades beginning next week.

His comments came on the fourth day of a national strike - called by the main umbrella union - in protest at plans to export Bolivia�s huge natural gas reserves to the United States.

The protesters fear they will earn little from any exports, preferring instead for the gas to remain in Bolivia.

Resignation call

Evo Morales is used to speaking his mind as opposition leader and head of the country's coca growers.

Riot police have been deployed to disperse protesters

Last week, he went so far as to suggest that there were people who wanted him to win the Nobel Peace Prize.

But in an interview with Radio Panamericana, his comments were far from peaceable.

Speaking from Geneva, where he is attending the World Interparliamentary Union, Mr Morales once again called for President Gonzalo Sanchez de Lozada, to step down.

If he failed to do this, Mr Morales said, there were many other "exits" for the President, and he didn't rule out removing Mr Sanchez de Lozada by force.

He said things had got so bad that the United Nations should intervene, though with the government still largely in control of the country, this seems unlikely.

'Failed policies'

Calls for the president to resign have grown in recent days, amid anger over his failed economic policies and plans to export the country's natural gas to the US.

In their latest attempt to get the government to heed their demands, demonstrators tried to block the main road linking La Paz with its airport in the neighbouring city of El Alto.