Greece is poised to send Germany a formal diplomatic note detailing its demand for billions of euros in wartime reparations after MPs voted overwhelmingly for the emotive issue to be raised officially.

In a move bound to stir sentiment ahead of crucial European parliament elections, Athens vowed to pile pressure on Berlin, taking legal and diplomatic steps that will throw the spotlight on crimes committed during the brutal Nazi occupation.

“It is an open issue that must be resolved,” Greece’s deputy foreign minister, Markos Bolaris, told the Guardian, hitting back at German insistence that compensation claims had been conclusively settled.

“For matters of this kind there is international justice,” he said on Friday. “In all disputes the EU abides by it, on principle. Germany may say it has been resolved but what counts is international law.”

Greeks suffered hugely at the hands of Hitler’s forces, enduring what Germany’s president, Frank-Walter Steinmeier, recently described on a visit to Greece as “unimaginable” horrors.

Tens of thousands were killed in reprisals as Greeks mounted what historians would later hail as a heroic resistance against the Wehrmacht [Nazi armed forces], with entire villages being wiped out between 1941 and 1944.

By the time the occupation ended, an estimated 300,000 people had died from famine and the country’s Jewish community had been almost entirely obliterated.

The prime minister, Alexis Tsipras, has raised the issue more persistently than any other to date.

Despite criticism of political opportunism as European polls near, Greek MPs this week backed a resolution calling for the government to pursue demands for €300bn in damages following debate on the findings of an all-inclusive parliamentary inquiry into the German occupation. The findings have been described as the first complete reading of Nazi atrocities in Greece.

In its report – compiled after in-depth research of records obtained from US national archives and Russia – the cross-party committee estimated that €11bn was owed for an interest-free “occupation loan” forcibly extracted by German forces.

Gold holdings, seized from the country’s central bank in 1943, were used to fund Germany’s campaign in north Africa. A further €288bn, it said, remained outstanding for the destruction Greece sustained during the war.

Berlin has long argued that recompense was delivered when, under a bilateral accord, it paid Athens DM115m in 1960.

But addressing the Greek parliament, Sia Anagnostopoulou, the minister who will be heading the compensation campaign, described the reimbursement as inadequate.

“The agreement did not take into account the occupation loan or reparations … they concerned individuals, victims of the Nazis,” she said, adding that the Netherlands had received a much greater sum despite having “one-hundredth” of the total number of victims of Greece.

“There is an issue here with the German people and the German government with whom we are friend and allies, and we must not forget that.”

Leftist MPs have long claimed that Greece’s brutal wartime experience delayed its development as a modern European state.

The issue of war crimes reignited with renewed passion with the eruption of Greece’s debt crisis in late 2009 when Germany, as Europe’s paymaster, imposed punishing austerity measures as the price of emergency loans to keep the insolvent country afloat.

At its height, the German chancellor, Angela Merkel, was depicted in Greece in Nazi garb, wearing a swastika armband, with many Greeks drawing comparisons to the time when they lost sovereignty under Nazi rule.

Although Tsipras has since tempered his rhetoric, forging visibly warm relations with the German leader, the question of war debt is likely to gain traction as Greece gears up for general elections later this year.

Prior to Athens exiting its third and final bailout last summer, officials say it would have been “nonsensical” to have raised the issue.

Indicative of the emotions Nazi-era crimes are still prone to elicit, within hours of the vote in the Greek parliament, the MP in charge of Warsaw’s reparations campaign announced that Poland should follow suit.

Greek compensation claims pale by comparison. Warsaw was razed to the ground by the Nazis after an abortive uprising in which 200,000 civilians died. The lives of 6 million Poles – including 3 million Polish Jews – were lost. Poland, which also faces parliamentary elections this year, has since demanded €800bn in war debts it insists it is still owed by Germany.

• This article was amended on 22 April 2019. Due to an editing error an earlier version incorrectly translated Wehrmacht as “German army”.