The U.S. embassy in Madrid on Thursday received a letter which resembles letter bombs sent to other targets in Spain, according to local media reports. The alarming news comes the day after the country’s Ukrainian ambassador was targeted with a device in the same city, with a member of the Ukrainian embassy staff who handled the letter being slightly injured when it exploded. Another of the potentially deadly packages found last week had been addressed to Spanish Prime Minister Pedro Sánchez Pérez-Castejón, local law enforcement said earlier on Thursday, though the threat was intercepted and neutralized last week before it reached him. On Thursday morning, a similar package was found in central Spain at the Torrejón de Ardoz air base—the site from which flights ferrying Spanish aid to Ukraine have departed in recent months. Another explosive letter was found Wednesday evening at a factory in the northern city of Zaragoza where grenade launchers are being manufactured to be shipped to Ukraine. It’s not yet clear if the letter received at the U.S. embassy is a legitimate threat, and no injuries have been reported.