MADRID (AP) — Spain's interior ministry said Wednesday police had arrested a man on suspicion of sending six letters containing explosive material to Spain’s prime minister and to the U.S. and Ukrainian embassies in the country.

The Spanish national was arrested in the northern city of Miranda de Ebro and a search of his home is “still underway,” the ministry added in a statement.

An employee at the Ukrainian embassy in Madrid was slightly injured while handling a letter in November. A bomb squad also destroyed an explosive device that was dispatched by regular post to Spanish Prime Minister Pedro Sánchez in the same month.

Letters with similar characteristics were sent to Spain’s Defense Ministry, a European Union satellite center located at the Torrejón de Ardoz air base outside Madrid and to an arms factory in northeastern Spain that makes grenades sent to Ukraine.

An envelope intercepted at the American Embassy’s security screening point in December was detonated by authorities after a wide area was cordoned off by Spanish police around the embassy in the center of Spain’s capital.