Von der Leyen aims to 'rebalance Europe'

"We all know that problems can only be addressed if we are united, successful and strong. The world is calling for a strong European voice, and this can only be achieved if we are together," she added.

She called Croatia a "tremendous success story," saying the bloc's newest member state serves as a role model for many other countries.

Germany's former defence minister, who takes up her post in Brussels on 1 November, has met with EU leaders, who picked her as the new commission president early July after a marathon summit - despite the lead candidates put forwards by European Parliamentary groups.

Countries have until 26 August to nominate their commissioners to the new EU executive, and national leaders - who have helped the German get the top job - are jostling to secure important portfolios for their nominees.

Von der Leyen has so far visited Berlin, Paris and Warsaw, and travels next to Spain and Italy. Von der Leyen has also met Czech premier Andrej Babis in Brussels and will meet with Hungary's Viktor Orban on Thursday (1 August).

Plenkovic, who hails from the same centre-right political alliance, the European People's Party (EPP), as von der Leyen and who was also touted for a top Brussels position, has supported von der Leyen's nomination.

Croatia's is set to take over the EU's rotating presidency in January.

Von der Leyen hailed Croatia's efforts to join the eurozone and the border-free Schengen area since becoming an EU member in 2013. Croatia's bid will need unanimous backing from EU countries. "I am at your side to proceed in that," von der Leyen said.

Croatia and neighbouring Slovenia have also been locked in a border dispute, which could create hurdles for Zagreb.

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Von der Leyen's nomination to the top job was made possible after fierce opposition to the nomination of Social Democratic lead candidate Frans Timmermans from some central European countries, such as Poland and Hungary, and from Italy.

The EU has launched ongoing probes into the rule of law of Hungary and Poland. Their enthusiasm for von der Leyen has raised questions of the German politician will keep up the pressure on the two nationalist governments for breaching EU rules.

The 60-year-old woman - the first female leader to head the commission - has earlier called for more understanding for countries such as Poland and Hungary when it comes to the rule of law, telling the German daily Suddeutsche Zeitung daily that "nobody is perfect".

It is still unclear if Timmermans, who is expected to remain vice president of the commission, will hold onto the rule of law portfolio, or if von der Leyen prefers to give that to a commissioner from the central and eastern European member states to avoid the perception of western countries imposing their rules on eastern member states.

Von der Leyen will meet with Hungary's Orban on Thursday when they expect to discuss the country's new commissioner, expected to be Laszlo Trocsanyi, former justice minister, current MEP, and the country's priorities for the next years.

The names of Fidesz MEP Eniko Gyori and Livia Jaroka have also been floated as possible back up candidates to Trocsanyi.

Orban claimed over the weekend to have "prevented ideological guerrillas from being installed at the head of important European institutions".

"To lead the commission we've succeeded in choosing a mother-of-seven who has a practical approach," Orban told a summer camp in Romania, referring to von der Leyen, where he yearly makes broad ideological speeches.

"This commission must return to its role as laid down in the founding treaty of the European Union: to act as the guardian of the treaties.

"And it must abandon its political activism. It is not a political body: it is not its remit to have a programme, and it is not its remit to launch political attacks on member states," Orban said as he laid out his expectations form von der Leyen, saying this sort of commission has now become possible.

"For it's obvious that the strategic-political direction of the European Union is not determined by the commission, but by the leaders of the member states' democratically elected governments: heads of state or prime ministers," he added.

"And the commission must remain an organisation subject to the influence of the prime ministers," Orban said.

He added that migration should be taken away from the commission and should be dealt with by a special council of ministers, like the eurogroup for the euro currency.

He also said, "instead of migrants, European families must be given the money to enable them to commit to having as many children as possible".