A pro-Russian seperatist stands guard at a check point in eastern Ukraine | Andrew Burton/Getty Images France, Germany urge cease-fire in Ukraine as violence flares Following talks with Russian and Ukrainian leaders, Europeans warn of humanitarian catastrophe.

PARIS — The leaders of France and Germany called Tuesday for an immediate ceasefire in eastern Ukraine, where violence flared again in July despite years of attempts to stop the conflict.

Warning of a possible "humanitarian catastrophe," French President Emmanuel Macron and German Chancellor Angela Merkel called for withdrawal of all forces and heavy arms from disputed areas in eastern Ukraine following a four-way "Normandy format" call Monday with the leaders of Russia and Ukraine.

The Franco-German plea came after more than two years of efforts to broker a cease-fire in Ukraine, underscoring the limits of a four-way negotiation format inaugurated on the sidelines of a G20 summit in France, back in 2014.

It also came as the new U.S. special envoy for the crisis in Ukraine, Kurt Volker, said Washington is actively considering whether to send lethal weapons to Ukrainian government forces.

"The cease-fire violations must stop immediately," Merkel and Macron said in their statement. "Necessary measures must be taken so that civil infrastructure and essential buildings stop being struck in order to avoid a humanitarian catastrophe in the Donbas," they said.

Despite years of talks and ongoing EU and U.S. sanctions against Moscow — Washington may soon reinforce theirs — the Crimean Peninsula, which after the fall of the Soviet Union became part of an independent Ukraine, remains in Russian hands.

Ukrainian troops and Russian-backed separatists continue to fight in the country's disputed east. And on July 20, Ukraine announced that eight government troops had been killed and 10 wounded, its worst toll yet this year.

In his own readout from the Normandy call, Ukrainian President Petro Poroshenko pressed Russia to cease "aggressive actions," stop the supply of weapons to occupied territories and let United Nations monitors into Donbas.

France and Germany also pressed the warring parties to let monitors from the Organization for Security and Cooperation in Europe into all conflict zones so they could verify withdrawals and compliance with cease-fire agreements. Neither side has fully complied with previously-agreed de-escalation measures.

The Kremlin issued a separate statement that made no mention of the uptick in violence and called the fighting an "internal Ukrainian conflict."

The United States Congress is due to examine legislation that would toughen sanctions against Russia and curtail President Donald Trump's ability to lift them.

The White House this week issued mixed messages on whether or not Trump was ready to support the new sanctions bill, with spokespeople Sarah Huckabee Sanders and Anthony Scaramucci making divergent statements on Trump's intentions.

The US sanctions would penalize firms, including European companies, that contribute to Russian energy development. The prospect prompted a threat of retaliation from European Commission President Jean-Claude Juncker.

However, Juncker needs member countries' support to level any penalties against the United States, and EU member nations are divided in their approach to Russia. Some eastern EU countries in particular are opposed to retaliation, as they do not support projects that reinforce European dependence on Russian gas.