The announcement accelerates a previous timeline that set 2029 as the target year to reach the benchmark agreed by NATO allies but deemed too low by US President Donald Trump.

Russia's three-year-old invasion of Ukraine and Trump's questioning of decades-long US security guarantees have seen Europe scramble to design new defence strategies with bigger budgets in the quest for greater autonomy.

"It is essential that we meet the investment targets our partners demand," Sanchez told a news conference as he announced plans to spend 10.47 billion euros ($12 billion).

The aim is to "consolidate Spain as a central and trustworthy member of the European Union and the Atlantic alliance in a world dominated by uncertainty", the Socialist premier added.

Spain dedicated 1.28 percent of its annual economic output to defence last year, a lower proportion than any other member, according to NATO figures.

Sanchez's minority government relies on small far-left groups and separatist parties traditionally hostile to NATO and alignment with US foreign policy, complicating his efforts to hike defence spending.

Spanish media reported that the Socialists' far-left junior coalition partner Sumar fiercely opposed the move during Tuesday's cabinet meeting.

Attempting to assuage such concerns, Sanchez said the new cash would come "without raising taxes, without touching a cent of investment in the welfare state and without incurring a larger public deficit".

Less than one-fifth of the new investment will go towards "the purchase of armaments in the most traditional sense of the term", while almost one third will be ploughed into "acquiring new telecommunications and cybersecurity capabilities each year", he added.

A further 17 percent of the plan will "strengthen the dual capacities" of the army to help manage emergencies and natural disasters, he announced.

It was unclear whether NATO would accept counting that money as part of annual defence spending.

Sanchez confirmed the spending plan would not be submitted to a vote in parliament, infuriating the main conservative opposition Popular Party, which called it "not serious or democratic".