Mexico said Thursday that it will file a complaint against the interim government of Bolivia at the International Court of Justice at The Hague.
Marcelo Ebrard, Mexico's foreign relations secretary, said the buildup of Bolivian agents around the Mexican Ambassador's residence violates international treaties regarding the rights and protections for diplomatic personnel and installations.
Bolivian agents surrounding the residence appear to threaten Mexico's right to give asylum to nine former officials of ousted president Evo Morales, Ebrard said.
He said Bolivian authorities had refused to allow any of the nine to leave the country.
Since Nov. 15, a group of ex-Cabinet ministers and others loyal to former Morales have sought refuge at the Mexican ambassador's La Paz residence.
Troops gathered in larger numbers around the residence beginning Tuesday, the Mexican Foreign Ministry said. It also said drones were flying over its ambassador's residence and that it had summoned the top Bolivian diplomat in Mexico to "explain the actions of Bolivian officials."
Relations between the two countries have been strained since Mexico granted asylum to Morales after he resigned Nov. 10 following a national upheaval over his claim of victory in an election marred by vote-rigging.
Morales has since relocated to Argentina and says he plans to stay involved in politics in neighboring Bolivia, while some former top aides remain holed up in the Mexican ambassador's residence.
Willson Santamaría, Bolivia's deputy minister of public security, said the Morales loyalists would not be allowed to leave the country.
"We have taken the necessary steps so that the security forces immediately track and detect any help, any complicity in helping the fugitives flee the country," he said.
Those who sought refuge in the Mexican ambassador's residence include Juan Ramón Quintana, the former chief of staff for Morales, and five other former Cabinet ministers, according to a Mexican federal official. The official was not authorized to comment publicly about the matter and spoke on condition of anonymity.
At least four are accused by the interim government of President Jeanine Áñez of electoral fraud or other crimes.
Mexico has complained that Bolivian security forces are recording the movement of people in and out of Mexico's diplomatic facilities and even impeding the "free transit" of the ambassador.
Erick Foronda, Bolivia's presidential secretary, denied authorities are interfering with Mexico's diplomats.