The European Union on Thursday intensified legal action against Hungary in a bid to make it comply with EU asylum rules, denouncing a law to punish activists who support asylum seekers.

The European Commission, the EU's executive arm, has clashed repeatedly with Hungarian Prime Minister Viktor Orban's government, especially since the migration crisis erupted in 2015.

The clashes come amid broader fears that Hungary, Poland and other eastern countries from the former Soviet-bloc were turning away from the democratic values on which the EU is built.

The commission denounced as illegal the so-called "Stop Soros" laws passed last month, which include a punishment of up to a year in prison for anyone assisting any other person who entered Hungary illegally.

It sent a "letter of formal notice" to Budapest, the first step of a procedure that could go before the European Court of Justice, the bloc's top tribunal.

"The Hungarian authorities have two months to respond to the Commission's concerns," the commission said.

The legislation was dubbed the "Stop Soros" laws after liberal US billionaire George Soros, accused by Orban's government of orchestrating migration to Europe.

In other action, the commission said it was taking Hungary to the top court for failing to resolve complaints made in December 2015 that it held asylum seekers for too long in transit centres and did not treat them properly.

"The border procedure implemented by Hungary is not in compliance with EU law as it does not respect the maximum duration of four weeks in which someone can be held in a transit centre," the commission said.

In violation of EU rules, it added, irregular migrants were escorted back across the border even if they want to apply for asylum.

Following US President Donald Trump's administration, Hungary said Wednesday it was withdrawing from a UN pact on migration, saying that the global deal encourages movements of people which are "dangerous for the world."