Spanish police have intercepted another batch of threatening letters addressed to Ukrainian diplomatic offices in Spain.

On Monday morning, three suspicious envelopes were detected and intercepted by security systems at a Spanish post office, although police quickly ruled out the presence of explosives, as have been used in letter bombs across Spain in recent weeks.

It was instead confirmed that they contained animal eyes.

Spanish media reports claim that according to sources from Spain’s Interior Ministry, the letters were first detected on Friday and the National Police passed on details to the postal service.

The three suspicious envelopes were addressed to the Ukrainian embassy in Madrid, and consulates in Barcelona and Málaga.

These latest deliveries continue a trend of sinister letters sent in Spain in recent weeks. Letter bombs have been sent to the Ukrainian embassy in Madrid, and also the Spanish Prime Minister Pedro Sánchez in late-November. 

Further letters containing explosives were also intercepted at the Torrejón de Ardoz airbase on the outskirts of Madrid, somewhere regularly used to send Spanish weapons to Ukraine. 

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Other letter bombs were also sent to Spain’s Ministry of Defence in Madrid, the US Embassy in Madrid, and at the headquarters of military equipment firm Instalaza in the northeastern city of Zaragoza, according to the Interior Ministry.

Instalaza manufactures the grenade launchers Spain have donated to the Ukrainian war effort.

Ukraine’s spokesman for the Ministry of Foreign Affairs, Oleg Nikolenko, has confirmed the latest three envelopes containing animal eyes, and that there are now 21 cases in which threatening packages have been sent to Ukrainian diplomatic buildings in 12 countries.

Last week the Ukrainian Embassy in Lisbon received two suspicious envelopes that were ultimately found not to contain explosives.

On Saturday, a source close to the police investigation revealed to Reuters that at least six of the letter bombs were likely posted from the city of Vallodolid in northern Spain.