LA PAZ, Bolivia — Embattled President Gonzalo Sanchez de Lozada will resign after weeks of deadly street riots triggered by a government plan to export natural gas, a close presidential ally said Friday.

Sanchez de Lozada said he would issue a statement late Friday afternoon. His government coalition received a crippling blow earlier Friday as his last key supporter withdrew after weeks of countrywide street demonstrations.

Jaime Paz Zamora, a former president himself, called the impending announcement by Sanchez de Lozada a "patriotic decision."

Asked by reporters whether he meant a presidential resignation, Paz Zamora responded, "You are intelligent people. You know what it is."

Thousands of Bolivians marched through La Paz for a fifth straight day Friday, demanding that Sanchez de Lozada, 73, step down 14 months into his second term.

Columns of students, Indians and miners brandishing sticks of dynamite threaded past street barricades, shouting, "We will not stop until he's gone!"

Also Friday, military planes airlifted hundreds of stranded foreigners from Bolivia's capital.

The president temporarily suspended the gas export plan last week in the face of riots, which human rights groups said claimed as many as 65 lives.

His increasingly fragile coalition suffered a key blow Friday when Manfred Reyes Villa, a key presidential supporter in congress, said he was quitting the government after weeks of deadly riots between troops and Bolivian Indians carrying sticks.

"I've come to tell him: 'No more,' " Reyes Villa said. "The people don't believe in this government anymore and there is no other option but for him to resign."

On Thursday, presidential spokesman Mauricio Antezana also resigned.

Reyes Villa's departure left the president isolated as he sought to defuse the crisis in this Andean country of 8.8 million people, South America's poorest.

Late Wednesday, the president sought to defuse the growing crisis with a nationally televised address in which he offered to hold a national referendum vote over the plan. But opponents rejected that offer.

A U.S.-educated millionaire, Sanchez de Lozada was president from 1993 to 1997. He took office for a second term in August 2002 after narrowly defeating Evo Morales, a radical congressman.

For days, the main highway link between La Paz and El Alto has been lined with hundreds of demonstrators clutching rocks and sticks and burning barricades.

A Peruvian air force plane also evacuated 80 stranded Peruvians to the Andean city of Arequipa on Friday and planned to return to Bolivia to shuttle more people out, a Peruvian cable news channel reported.

Several countries, including Canada, Britain and the United States, were advising citizens not to travel to Bolivia because of deteriorating security. Those already in Bolivia were urged to keep off the streets, refrain from travelling and avoid demonstrations.