Vienna/Brussels (dpa) - The leaders of six European Union countries called on Saturday for high-level EU talks on the equitable distribution of coronavirus vaccine doses, saying that the current system would create "huge disparities" among member states by the summer.

The leaders of Austria, Bulgaria, the Czech Republic, Latvia and Slovenia said in a letter to EU officials that the current system "would continue creating and exacerbating huge disparities among member states by this summer, whereby some would be able to reach herd immunity in a few weeks, while others would lag far behind."

Croatia also joined the initiative later on Saturday.

The letter, addressed to EU Council President Charles Michel and Commission President Ursula von der Leyen, called on EU officials "to hold a discussion on this important matter among leaders as soon as possible."

According to the bloc's vaccine strategy, all EU countries get access to approved shots at the same time, with distribution of available doses linked to population size.

But Austrian Chancellor Sebastian Kurz said on Friday that doses were not being handed out proportionally among EU member states, as additional supply contracts were being agreed as the result of non-transparent negotiations in an EU steering group.

According to Kurz, Denmark and the Netherlands have access to significantly more vaccine doses per capita than countries like Bulgaria or Croatia.

The European Commission negotiated vaccine supply contracts with pharmaceutical companies on behalf of the 27 member states, which could opt in or out of each pre-order and choose how many doses to buy.

EU officials confirmed receipt of the letter. "We are closely monitoring the situation," one EU official said, pointing to a summit planned for March 25-26 to address Covid-19 coordination.

On Saturday, the Netherlands rejected Austria's allegations that it had procured additional vaccination doses outside the scope of EU agreements.

The country receives vaccines through the designated EU mechanism, but makes use of leeway granted by the bloc, a Health Ministry told dpa.

If a country waives its right to its full allocation, other countries can gain access to it, as the Netherlands had done, the spokesperson pointed out.

Around 1.4 million residents of the Netherlands have received at least one vaccine dose so far. More than 400,000 have already received both jabs, which corresponds to about 2.5 per cent of the population.

Malta also rejected similar allegations. Maltese Health Minister Chris Fearne said the country had procured its doses through the EU distribution mechanism.