Brussels (AFP) - The EU and NATO called on Russia to end its support for rebels in Ukraine, with Brussels mulling an emergency meeting after at least 30 people were killed in the port of Mariupol in a major escalation of the fighting.

Latvia, which holds the EU's six-month rotating presidency until July, called for an emergency meeting of the EU foreign affairs council next week.

The Latvian foreign ministry said it was increasingly evident that Russia "is not interested in a peaceful resolution of the conflict" in Ukraine in light of events in the strategic city of Mariupol.

"Those responsible for the aggression should be aware that the international community will undoubtedly and sharply react to further escalation," the ministry said in a statement.

NATO Secretary General Jens Stoltenberg urged Russia to "stop destabilising Ukraine and respect its international commitments".

"Fighting in eastern Ukraine has sharply escalated, with indications of a large-scale offensive by Russian-backed separatists," he said in a statement. "This is in utter disregard of the ceasefire."

The NATO chief added that "for several months we have seen the presence of Russian forces in eastern Ukraine" -- a charge Moscow has repeatedly denied.

The condemnation of the Mariupol attacks came after Alexander Zakharchenko, leader of the self-declared Donetsk republic, on Saturday announced an offensive on the Kiev-controlled port, which links separatist territory with Russian-occupied Crimea.

EU foreign affairs chief Federica Mogherini denounced Saturday's rocket attacks on Mariupol saying in a statement that the escalation would cause a further deterioration in relations between the EU and Russia.

Mogherini called directly on Russia to intercede.

"I call... openly upon Russia to use its considerable influence over separatist leaders and to stop any form of military, political or financial support," her statement said.

"This would prevent disastrous consequences for all. Those responsible for the escalation must stop their hostile actions and live up to their commitments."

The European Union, along with the United States, has imposed sanctions on Moscow over its role in the Ukraine crisis.