NOVO-OGARYOVO, Russia (AP) — The leaders of gas-starved European nations pressed Ukraine and Russia to restore energy supplies immediately Wednesday and the European Union threatened that they both could be sued for ripping apart the continent's winter heating plans.

But the natural gas drought persisted along with virulent, mutual recriminations between Russia and Ukraine.

In an indication that no resolution was on the horizon, Russian President Dmitry Medvedev proposed that European gas-consuming nations send their leaders to Moscow for a summit this Saturday.

The prime ministers of Bulgaria and Slovakia — among the hardest-hit nations — showed up in Moscow and Kiev even before the summit call.

"Millions of Europeans feel like hostages and are truly suffering," Bulgarian Prime Minister Sergei Stanishev told Vladimir Putin as he visited the Russian prime minister's home outside Moscow with his counterparts from Slovakia and Moldova.

Both Medvedev and Putin accused Ukraine of being responsible for holding Europe hostage, while Kiev said Russia was deliberately erecting technical obstacles to delivering gas to Europe through Ukrainian pipelines.

The Ukrainian president, Viktor Yushchenko, insisted the Russian gas monopoly Gazprom was trying to charge Ukraine an unjustly high price for gas in order to drive it into debt and acquire a stake in Ukraine's vast pipeline network. Visiting Poland on Wednesday, Yushchenko vowed he will never let that happen.

Calling the situation "incredible," European Commission President Jose Manuel Barroso warned Gazprom and Ukraine's state-run company Naftogaz he will urge European energy companies to sue them unless the dispute was resolved quickly.

"If the agreement is not honored, it means that Russia and Ukraine can no longer be considered reliable partners for the European Union in matters of energy supply," Barroso told the European Parliament.

The crisis has deepened European concerns about Russia's willingness to use its energy riches as a political tool and raised questions about the reliability of Ukraine, whose pro-Western leaders want to join the EU but are mired in dangerous disputes with Russia.

European Union countries had hoped supplies would be restored Tuesday after they brokered a deal sending EU monitors to keep tabs on the flow of gas. Europe relies on Russia for about a quarter of its gas, 80 percent of that delivered via Ukraine.

But while Russia's gas monopoly Gazprom resumed some gas supplies, Ukraine did not send the gas on to Europe, saying the route that Gazprom demanded would force Ukraine to halt domestic gas supplies to a large swath of territory.