The European Union’s executive arm has recommended opening formal membership talks with Ukraine and Moldova.
The decision to move ahead with Ukrainian membership is seen as a key show of support amid the war with Russia.
At the same time, Turkey’s hopes of joining appear to be at a standstill, while Georgia received positive news on its membership bid.
“Today is a historic day. Ukraine continues to face tremendous hardship and tragedy provoked by Russia's war of aggression and yet the Ukrainians are deeply reforming their country,” Ms von der Leyen said.
The recommendation is an important milestone on the road to western integration and a geopolitical gambit for the EU.
The commission said talks with Ukraine should only start once it has addressed corruption, lobbying concerns and a law on national minorities within its borders.
“Today, the history of Ukraine and the whole of Europe has made the right step. Our country should be in the European Union,” President Volodymyr Zelenskyy said.
“Ukrainians deserve it both for their defence of European values and for the fact that even in times of full-scale war, we keep our word by developing state institutions,” he added.
Turkey's bid, which began in 2005, has barely advanced in recent years. Ankara's progress report made grim reading despite the bloc's reliance on Turkey to stem migration into Europe.
The commission has noted “serious deficiencies in the functioning of Turkey’s democratic institutions”.
EU leaders are expected to decide on whether to accept the commission's recommendation at a summit next month.
“EU enlargement is a driving force for long-term stability, peace and prosperity across the continent,” the commission's report said.
“It is a powerful tool to promote democracy, the rule of law and respect for fundamental rights,” it added.
Germany will thoroughly examine the commission's recommendation to start membership talks with Ukraine before making a decision, a government spokesperson said.
Moldova's bid also has conditions to meet, including significant progress in supreme court appointments and anti-corruption measures.
Georgian President Salome Zurabishvili welcomed the commission's recommendation to grant her country candidate status.
EU officials see the Georgian government as more inclined towards doing business with Moscow and regressing on its path towards membership in the western bloc.
Ms von der Leyen said the reforms needed are steps “that mirror the genuine aspirations of the overwhelming majority of its citizens to join the European Union”.
The commission also recommended the bloc begins membership talks with Bosnia and Herzegovina “once the necessary degree of compliance with the membership criteria is achieved”.
If Ukraine membership talks do start, it will be the beginning of a painstaking process of reforms that could last for years before it joins the EU.