Spain has stepped up security after revealing that a number of letter bombs have been sent to high-profile targets, including the Prime Minister, according to a media report.
On Wednesday, an employee of the Ukrainian embassy in Madrid was injured when a similar device exploded, BBC reported.
Officials say the Defence Minister was among the other targets. Another device was also sent to the US embassy, BBC reported.
It is thought the bombs could be linked to Spain's support for Ukraine, but no-one has yet claimed to have sent them.
Russia - which invaded Ukraine in February - has condemned any "terrorist" activity, saying such threats or acts were "totally reprehensible", BBC reported.
On Thursday afternoon, the US embassy in Madrid confirmed that it too had received a "suspicious package" - thanking the security forces for their help in dealing with it.
The Spanish government had earlier said that explosive devices had been sent to five targets.
It said an envelope containing pyrotechnic material had been sent to Prime Minister Pedro Sanchez, but was intercepted on 24 November before anyone was hurt.
This was said to be similar to packages sent to the Defence Minister, a weapons manufacturer in Zaragoza, and the Torrejon Air Base - and to the Ukrainian embassy in Madrid.
A male worker at the Ukrainian embassy was taken to hospital after being hurt when he opened the letter bomb, but Ukraine said his life is not in danger.
Spain is investigating the incident as a possible terrorist act, while Kiev responded by pledging to tighten security at its embassies around the world, BBC reported.
In a press conference, a minister said the envelopes were being analysed, and that all five appeared to have been sent from somewhere within Spain.
There is speculation that the bombs are connected to Spain's strident support for Ukraine during its war with Russia, BBC reported.