Both Barcelona and Milan were candidates to host the European Medicines Agency (EMA) when it departs the UK, but while the Catalan capital was eliminated in the early rounds of the voting process, the Italian city made it to the final two.
Milan tied with Amsterdam in the last round as both had the same number of votes, and the ultimate decision was then made by drawing lots, resulting in a Dutch win.
According to Italian news agency ANSA, which cites sources close to the matter, the Milan candidacy felt betrayed by Spain because the latter cast its final vote in favour of Amsterdam, despite a reported agreement between the two Mediterranean governments to vote for each other if one of their cities was eliminated in a previous round.
Lombardy regional president Roberto Maroni supported that claim while speaking to the media on Tuesday, saying Italian PM Paolo Gentiloni was "very angry" with Spain's decision to vote for Amsterdam and "rivalry and resentment won over strategy".
Maroni, a member of the far-right Northern League which campaigns for further regional autonomy, threatened to give greater backing to the Catalan independence movement in retaliation: "We will more strongly support Catalonia in its demand for autonomy and independence".
Madrid denied having an agreement with Italy, however, and instead said it made a deal with the Netherlands. "We reached an agreement with the Netherlands and also spoke about the possibility of reaching one with Italy, but never closed it, so what we did was fulfil our commitment," Spain's Foreign Minister Alfonso Dastis told news agency Europa Press.
Dastis added that he was unaware of any unhappiness on the part of the Italian government.
The failure of Spain's own candidacy has been the subject of debate at home. The central government blames Catalonia's independence drive, while separatists said it was Madrid's heavy-handed approach in quashing the independence movement that caused the loss.
The EMA also caused a further diplomatic bust-up in northern Europe, with Denmark's foreign minister saying earlier this week that Sweden had "let down" its Nordic neighbour in the voting process.
READ ALSO: Sweden let us down in EMA vote, Denmark says