A pro-European presidential contender in Romania's May 4 election has said defence spending should rise to 3.5% of GDP by 2030 from 2.5% and argued that maintaining support for Ukraine in its war with Russia is essential for Romania's security.

Nicusor Dan, the 55-year-old two-term mayor of Bucharest, is an independent running neck-and-neck with ruling coalition centrist Crin Antonescu and nationalist former prime minister Victor Ponta in a bid to reach a runoff on May 18, alongside the hard-right frontrunner George Simion.

Dan is running on an anti-corruption platform, something also likely to find favour with European Union and NATO allies as Romania assumes growing importance as a bulwark against Russian influence on the border with Ukraine and Moldova, another state under pressure from Moscow.