By Gram Slattery and Daniel Ramos

LA PAZ (Reuters) - Bolivian security forces clashed on the streets of La Paz with supporters of unseated president Evo Morales on Wednesday, firing tear gas to clear crowds who hurled rocks and set fires in a test to Bolivia's new interim leader.

With Morales thousands of miles away in Mexico City after he resigned under pressure on Sunday, crowds of his supporters carrying colorful flags and banners marched in the capital while his party's lawmakers looked to unseat Jeanine Anez, the Senate vice-president who stepped in on Tuesday.

Anez, 52, said she wanted elections as soon as possible and denied a coup had taken place against leftist leader and newly-exiled Morales, who hinted he could return to Bolivia.

Morales' 14-year socialist rule ended in violent protests and recriminations after rising pressure over accusations of vote rigging in the Oct. 20 election. But he struck a defiant tone from Mexico where he is seeking asylum.

"If my people ask, we're ready to go back. We'll return sooner or later ... to pacify Bolivia," he said at a news conference in Mexico City.

Anez, who has already overhauled some of Morales' policies, faces a challenge from lawmakers of Morales' Movement for Socialism (MAS) party, who have a majority in parliament and have threatened a rival session to nullify her presidency.

The religious conservative arrived to take on her new role carrying a bible in a symbolic break from indigenous leader Morales. She has already recognized Venezuelan opposition leader Juan Guaido over Morales ally President Nicolas Maduro.

Anez was forced to declare herself president after legislators from the MAS party boycotted her swearing in. She instead invoked a constitutional clause as the next person in line for succeeding the president.

But Morales' loyalists say that move was illegal because Congress did not formally accept Morales' resignation, and tried to hold a counter meeting on Wednesday.

Large numbers of police around the central Plaza Murillo in La Paz appeared to block MAS lawmakers, including former Senate head Adriana Salvatierra, from entering the government building.

Salvatierra had resigned publicly but said on Wednesday that her resignation letter had not been formally accepted. "I'm still a senator," Salvatierra told journalists.

SPLIT VIEWS ON ANEZ

Police also fired tear gas in the city center to break up crowds after thousands of Morales supporters marched into La Paz from nearby El Alto, many carrying the colorful "Wiphala" flags of regional indigenous groups.

Many previously marginalized indigenous groups saw their power and affluence rise significantly under Morales, a former coca grower who was Bolivia's first indigenous president.

Bolivia's Attorney General says there have been at least seven fatalities in the 23 days of conflict, including in the cities of La Paz, Santa Cruz and Cochabamba.

People in La Paz were split on Anez. "She does not represent the people, but the big elites, the society that has money but does not represent the poor," said bread seller Ruth Moscoso.

Others cheered Anez taking over the interim role and hoped it would bring stability after weeks of protests.

"It seems she is going to act in a fair way and will get us out of this mess," Jose Clarens said on his way to a market.

At the government palace, where Anez later unveiled her core team of ministers, she said she planned to call elections "in the shortest possible time."

"I now call for a peaceful and democratic transition, revoking the conditions that had made us into a totalitarian country," Anez said.

In 48 hours of turmoil at the weekend, mutinous police climbed on station buildings and joined marches, allies deserted Morales, the Washington-based Organization of American States (OAS) declared his re-election was manipulated, and the military urged him to quit.

International reaction to the crisis is divided. Left-wing allies echoed Morales' allegations of a coup and others cheered his resignation as good for democracy.

Conservative-led Brazil, Colombia and Britain congratulated Anez. A U.S. official said Washington would "look forward to working with her and Bolivia's other civilian authorities as they arrange free and fair elections as soon as possible."

Anti-Morales protesters say the pressure built on him to a point of no return with increasing evidence of election tampering and that he had gone against the will of the people by seeking a fourth term when he lost a 2016 referendum on changing the constitution to allow him to run again.

But Morales promised to keep up the political fight. He attacked the OAS audit of the election and later said the "coup" was a U.S.-led political conspiracy.

(Reporting by Gram Slattery, Daniel Ramos, Miguel Lo Bianco and Monica Machicao in La Paz and Diego Ore in Mexico City; Writing by Adam Jourdan; Editing by Andrew Cawthorne, Rosalba O'Brien and Grant McCool)