The European Union's 28 member states on Tuesday approved the controversial Association Agreement with Ukraine that brings it closer to the West at a time of hostility between Kyiv and Moscow.

The EU said the deal would formally start on September 1.

"The Association Agreement is the main tool for bringing Ukraine and the EU closer together: it promotes deeper political ties, stronger economic links and the respect for common values," the European Council said in a statement.

The agreement will give "a new impetus to the cooperation in areas such as foreign and security policy, justice, freedom and security (including migration), taxation, public finance management, science and technology, education and information society," the statement added. 

Valdis Dombrovskis, one of the European Commissions vice presidents, said that EU-Ukraine relations had been strengthened by visa liberalization implemented earlier this year and the Association Agreement. 

Much of the agreement is already provisionally operational, including parts on trade and politics.  A 2016 referendum in the Netherlands, where voters rejected the deal, had slowed its formal acceptance.

The EU and Ukraine agreed on the accord in late 2014, nearly a year after pro-Western protesters ousted former president Viktor Yanukovych. Yanukovych had been negotiating the same deal but abruptly halted it in favor of joining Russia's trade bloc, leading to the protests - supported by Western countries including the US and Germany - that led to a change of government in Ukraine.

In the aftermath, Russia annexed Crimea in early 2014 and allegedly proceeded to back rebels in eastern Ukraine.

The announcement comes a day before an EU-Ukraine summit in Kyiv on Wednesday and Thursday.