Spain's prime minister was also sent a letter bomb, it was revealed on Thursday, 24 hours after an explosion at the Ukrainian embassy in Madrid.
Pedro Sanchez was sent it last week, according to Spain's interior ministry.
"An envelope containing pyrotechnic material was [...] detected and neutralised by the security services on November 24," a media statement read.
On Wednesday, an employee at the Ukrainian embassy was injured in a small explosion after he "handled a letter" reportedly addressed to Kyiv's ambassador in Madrid. He received minor injuries and went to hospital unassisted.
Authorities later confirmed that an explosive package was also sent to an arms factory in the northern city of Zaragoza. Police carried out a controlled explosion of the parcel at the factory, which makes grenade launchers donated to Ukraine.
Meanwhile, another letter bomb was found on Thursday at a European Union satellite centre at the Torrejón de Ardoz air base outside Madrid.
Explosive devices concealed in postal packages were also allegedly discovered at Spain’s Defence Ministry and at the US embassy building.
After Wednesday's incident at the Ukrainian embassy, Spanish police activated the anti-terrorist protocol and cordoned off the area.
Spain's National Court has opened a probe into the matter as a possible terror incident. Initial investigations suggest that all the packages were likely sent from within Spain.
Ukrainian Foreign Minister Dmytro Kuleba has ordered the strengthening of the security of all embassies, a spokesperson wrote on Twitter.
"Whoever is behind this explosion will not be able to intimidate Ukrainian diplomats or stop their daily work to strengthen Ukraine and counter Russian aggression," a statement added.
The Russian embassy in Spain has also released a statement on Twitter condemning the letter bombs.
"We declare that any threat or terrorist act, even more so directed against a diplomatic mission, is totally reprehensible."