Herrero had suggested that extended voting hours could clear the way for election fraud after night falls.

Lucena said Herrero had disturbed the "peace and harmony" that had so far marked the referendum campaign.

'Chavez order'

Al Jazeera's Mariana Sanchez, reporting from Caracas, said: "Herrero was taken from [his]  hotel by a group of men, some were in uniform and some were in plain clothes ... and deputies say that it was an order from president Hugo Chavez."

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A statement from Venezuela's foreign ministry said: "In line with instructions from the electoral power and guaranteeing the accustomed respect of human rights, European deputy Luis Herrero has been invited to leave the country,"

Herrero, a member of the Spanish Popular Party, left on a commercial flight to Sao Paulo in Brazil at 11pm (0330 GMT) on Friday, according to a ministry source.

The upcoming referendum could allow the president to seek re-election indefinitely.

Chavez says he needs to stay in power to oversee the completion of his social reforms but the opposition says the move would undermine democracy.

Herrero had earlier made critical comments about Chavez when talking to journalists.

"They [Venezuelans] should never be carried away when they vote by the fear that a dictator tries to impose in a premeditated way," Herrero said.

Jose Miguel Vivanco, the Americas director of Human Rights Watch, was expelled in September under circumstances similar to Herrero's.