Berlin/Belgrade (dpa) - June 15 is Europe's "D-Day" for tourism ahead of the crucial summer season, Italian Foreign Minister Luigi Di Maio said on Tuesday as countries were preparing to open up after three months of the pandemic lockdown.

Tourism is an important, if not the largest, generator of revenue for most European Mediterranean countries, such as Italy, Spain, Croatia, Portugal and Greece.

Europe was working towards "a new start" on that date, di Maio told broadcaster Rai, referring to a German plan to lift a travel warning for tourists planning to travel to 31 European countries from June 15.

The move will end an unprecedented directive against all international travel.

Alongside Germany's 27 fellow EU member states, the warning will also be lifted for Britain and the four non-EU members of the borderless Schengen zone, Iceland, Norway, Switzerland and Liechtenstein, according to a draft policy proposal seen by dpa.

The plan, contingent on continuing positive trends in the coronavirus pandemic, could be approved by Chancellor Angela Merkel's cabinet as early as Wednesday.

Germany's Foreign Ministry announced the current warning on March 17, adapting a measure otherwise reserved for troubled conflict zones and applying it to the entire globe, followed by a massive airlift operation to bring more than 240,000 stranded tourists back home.

The warning against all foreign travel is to be replaced by advice tailored to the risks in individual countries.

Berlin is pushing for a common EU standard for countries to assess the situation and could propose using a metric already in place within Germany to track local infection levels.

Under the method, a locality must turn to stricter measures if more than 50 new cases of novel coronavirus are reported per 100,000 people in a seven-day period.

The German draft paper says the European Commission should develop a procedure to evaluate protective measures taken.

Meanwhile, Croatia, Slovenia and Greece have already lifted some travel restrictions and revealed plans to do more based on bilateral agreements and the epidemiological situation in individual countries.

On Tuesday, Slovenia lifted entry restrictions for tourists from the EU and the Schengen zone, allowing anyone with a hotel reservation to freely enter the country, STA news agency reported.

Nationals from other countries must still go to quarantine, with some exceptions, most importantly for those in transit.

Slovenia on May 15 became the first in Europe to declare the Covid-19 epidemic to be over.

Greece, with the continued recovery of its still-fragile economy hinging on tourism, already published a list of countries, some of them non-EU, whose nationals will be allowed to enter without tests or isolation from June 1.

Croatia also said that it will open its borders without restrictions for tourists from multiple EU countries starting on Friday.