European Commission chief Ursula von der Leyen has insisted that new problems dogging the supply of AstraZeneca's vaccines can be resolved, after the group admitted it could deliver only half the expected amount to the bloc in the second quarter.

AstraZeneca said Tuesday its EU supply chains would only be able to deliver half of an expected supply of Covid-19 vaccines to the bloc in the second quarter -- but that it would look to make up the shortfall from elsewhere.

"The vaccine manufacturers are our partners in this pandemic and they have also never faced such a challenge," she told the German regional daily Augsburger Allgemeine.

"New questions are always arising that we can generally resolve amicably," she said on the eve of a virtual EU summit on the response to the Covid-19 pandemic.

Von der Leyen added that she advocated "working together with the companies to ensure global production is improved".

Meanwhile, reports have said AstraZeneca was "working to increase productivity in its EU supply chain" and would use its "global capability in order to achieve delivery of 180 million doses to the EU in the second quarter".

Approximately half of the expected volume is due to come from the EU supply chain while the remainder would come from its international supply network.

The announcement follows controversy over deliveries of the AstraZeneca-Oxford University jab to the European Union in the first quarter, which has caused tension between the bloc and the pharmaceutical company.

The UK government has vaccinated millions of Britons with the AstraZeneca jab since late last year. But the company only began shipping it to the EU in early February, after the bloc's drug regulator took its time over recommending its use.

Ahead of the EU's approval of the vaccine at the end of January, the company sparked fury among European leaders by announcing that it would miss its target of supplying the EU with 400 million doses, due to a shortfall at the firm's European plants.

The disagreement also caused diplomatic tensions with Britain, which definitively left the EU after 40 years of membership following a transmission period at the end of 2020 -- with Brussels implicitly accusing AstraZeneca of giving preferential treatment to Britain at the expense of the EU.