- Summary- Ukraine embassy official slightly hurt by one device- Defence ministry, arms manufacturer, air base also targetedMADRID, Dec 1 (Reuters) - Bomb disposal experts defused a letter bomb at the U.S. Embassy in Madrid on Thursday, the sixth such device sent to high-profile targets in a wave that prompted Spain to step up security and vow not to be deterred from supporting Ukraine.Since Wednesday, similar devices were also sent to the defence ministry, an air force base, a weapons manufacturer and the Ukrainian embassy - where a security officer was slightly injured.Defence Minister Margarita Robles, who was visiting the Ukrainian port city of Odesa on Thursday and met her Ukrainian counterpart Oleksii Reznikov, said the letter bombs would not deter Spain from supporting Ukraine's "just cause".Rafael Perez, the junior minister responsible for security, told a news conference that the homemade devices were sent in brown packages containing a flammable powder and tripwire that would generate "sudden flames" rather than an explosion.One device had been kept intact for investigative purposes, Perez said, while the others were detonated by the security forces in controlled explosions."