Ukraine on Wednesday ramped up security at its embassies abroad after Spanish police and government said an employee at the Ukrainian embassy in Madrid was injured opening a letter bomb.
The worker suffered light injuries and brought himself to the Hospital Nuestra Señora de América in Madrid.
The letter had not been detected by the Ukrainian Embassy's private security service.
Ukraine's Foreign Affairs Minister Dmytro Kuleba has ordered all Ukrainian embassies abroad to "urgently" strengthen their security, according to a statement from Ukraine's foreign ministry.
The minister also urged his Spanish counterparts to "take urgent measures to investigate the attack", the statement said, adding that whoever was behind the attack "will not succeed in intimidating Ukrainian diplomats or stopping their daily work on strengthening Ukraine and countering Russian aggression".
The letter, which arrived by ordinary mail and was not scanned, caused "a very small wound on the ring finger of the right hand" of the employee, Mercedes Gonzalez, the Spanish government's representative in Madrid, told broadcaster Telemadrid.
Detectives are investigating the incident, aided by forensic and intelligence investigators, Spanish police said. Spain's High Court will lead the investigation.
An officer at Ukraine's embassy to Spain declined to comment.
The residential area surrounding the embassy in northwestern Madrid has been cordoned off and a bomb disposal unit is deployed at the scene, state broadcaster TVE reported.