Spain pledged Saturday to send investigators to La Paz after its embassy staff were accused of trying to sneak into the Mexican diplomatic mission accompanied by several masked individuals, an action denounced by Bolivia as a violation of its sovereignty.

Both Spain and Mexico said the incident occurred on Friday during a Spanish diplomatic visit to the Mexican embassy.

Bolivia's foreign ministry said "people identified as staff members at Spain's embassy in Bolivia, accompanied by people with their faces covered, tried in a secretive and underhand manner to enter Mexico's diplomatic residence in La Paz".

"What was the motive for Spain's consular minister to visit the Mexican ambassador accompanied by people with their faces covered and presumably armed?" said Bolivia's Foreign Minister Karen Longaric in remarks to the press on Friday.

"Spanish embassy diplomatic and security staff in Bolivia are not authorised to carry firearms or wear attire that conceals their identity," she said.

Although the alleged intruders were stopped by Bolivian police, La Paz had complained to Madrid in a letter citing "abuse" of diplomatic privileges that constituted a "serious trampling of Bolivia's sovereignty", with copies sent to the EU, the UN and the Organization of American States.

The Spanish government said it would send ministry staff to investigate the incident in the Bolivian capital.

"The foreign ministry has agreed to open an investigation into the incidents which occurred during a visit by Spain's charge d'affaires to the Mexican embassy in Bolivia," it said, referring to Cristina Borreguero.

"We are going to send people from the ministry in Madrid for the investigation," a ministry spokeswoman told AFP.

Bolivian Foreign Minister Karen Longaric said Spanish staff had been kept from entering their embassy because they were inappropriately "hooded and armed"
Bolivian Foreign Minister Karen Longaric said Spanish staff had been kept from entering their embassy because they were inappropriately "hooded and armed" AFP / JORGE BERNAL

In Mexico City, the foreign ministry said the incident occurred as Borreguero and Spanish consul Alvaro Fernandez wrapped up a meeting with Mexican envoy Maria Teresa Mercado.

After their talks, Mercado accompanied the pair out to the terrace at the entry of the residence to wait for their official vehicles, which were parked outside.

But they did not turn up and neither Borreguero nor Fernandez were able to reach their drivers nor their security detail, a ministry statement said.

"On hearing shouting, Ambassador Mercado invited the two visitors to reenter the residence. At that point, the Spanish diplomats were informed that their vehicles had been stopped from entering."

When the Spaniards eventually got hold of the Bolivian foreign ministry, they were told to leave the embassy on foot to find their vehicles, but refused to do so without a security detail.

Eventually a Bolivian ministry car was sent to pick them up which arrived about an hour later, it said. The Mexican embassy's head of mission was later also stopped from entering and only allowed to pass on showing ID.

The Mexican mission has been at the centre of an ongoing diplomatic row with La Paz after it took in around 20 former top officials who served under ousted president Evo Morales.

Morales fled Bolivia last month after nearly 14 years in power following weeks of mass street protests.

The spat has seen Mexico accusing Bolivia's new interim government of "harassment and intimidation" for deploying a large contingent of police and intelligence officers outside the embassy.

Bolivia has been in turmoil since late October when Morales declared he had been re-elected following a disputed election marred by fraud. On November 10, after losing the army's backing, he resigned and fled to Mexico, and then to Argentina.