The former President of Ecuador, Lucio Gutierrez, has returned home from exile in Colombia only to be arrested.
Lucio Gutierrez says he is the constitutional president of Ecuador
Mr Gutierrez, who refuses to recognize his successor Alfredo Palacio and has pledged to regain power, faces charges of endangering national security.
He is reportedly being flown to the capital Quito by helicopter.
Mr Gutierrez was ousted by the Congress in April following street protests. He earlier renounced the asylum granted to him by Colombia.
After his arrest, the former president reportedly remained calm and said he respected the police.
"This is yet another demonstration that they are violating my rights," he added.
Mr Gutierrez's return could complicate a delicate political situation, observers say.
Mr Palacio was recently forced to give in to a strike in the oil-producing region, and is struggling to enact promised political reforms.
The BBC's Simon Watts say he is at the mercy of local politicians who control public life in Ecuador, and Mr Gutierrez's return coincides with a sense of crisis in the new government.
Before leaving Colombia on a chartered plane, Mr Gutierrez said he would "use all legal and constitutional means to retake power".
"The constitutional president, elected by three million Ecuadoreans, is Lucio Gutierrez, whether he is exile, in jail or wherever I am found," he told journalists there.
"I plan to show there was a coup and that the president [Alfredo Palacio] is usurping power."
Mr Gutierrez was stripped of his powers by congress in April.
He fled the country and spent time in Brazil and Peru before seeking political asylum in Colombia.
In July, a judge ordered his arrest on charges of being a threat to national security.