Brussels/Strasbourg, France  - The failure of Russia and Ukraine to deliver natural gas to the European Union despite repeated promises to do so is "unacceptable" and unjustified, the bloc's executive said Tuesday.

The European Commission believes that there is "no justification for these problems to continue" and Russia and Ukraine "have to realise that the situation is simply unacceptable," commission spokesman Johannes Laitenberger said.

The spokesman further warned that the credibility of both sides was now "on the line."

Moscow - Russia resumed supplies of gas to Europe on Tuesday as observer teams began measuring gas flows through Ukraine in an effort to mediate the ongoing standoff between Moscow and Kiev.

Ukraine's Naftogaz said it had received a fax from Gazprom informing it 76 million cubic metres of gas had been sent through the pipelines "at 10 am Moscow time" (0700 GMT), news agency Itar-Tass reported.

Brussels/Moscow/Kiev  - Russia should resume gas supplies to Europe via Ukraine on Tuesday, European Union officials and representatives from Russian state-owned gas monopolist Gazprom said Monday after a deal appeared to have been sealed in Brussels.

"If there aren't any obstacles ... gas transits can be renewed already tomorrow, at 8.00 am European time (0700 GMT)," Gazprom deputy chief Alexander Medvedev said during a visit to Brussels.

Brussels  - The European Union has not tried hard enough to wean itself from its dependency on Russian gas, and now it faces a tough struggle to restore its security.

That was the verdict of industry experts on Monday as EU leaders waited to see whether the Kremlin's latest promise to have the gas flowing to Europe by the morning would bear fruit.

Prague - An EU official Sunday signed a deal that allows international monitors to observe Russian gas flow via Ukraine, opening way for a renewal of gas deliveries to Europe, Czech officials said.

Speaking to reporters after returning from his mission in Russia and Ukraine, Czech Prime Minister Mirek Topolanek said that European Commissioner for Energy Andris Piebalgs inked the deal, which was signed earlier by Russian and Ukrainian vice-premiers.

Topolanek said that Russia reiterated its vow to open gas taps as soon as the deal is signed by all parties and observers are in their place as defined by the agreement.

Moscow/Kiev  - Ukraine joined Russia to approve a European Union initiative for international observers to monitor Russian gas deliveries via Ukraine, raising hopes of a possible end to a Kremlin embargo on energy supplies to Europe.

Ukrainian Prime Minister Yulia Tymoshenko signed the deal early Sunday, Interfax news agency reported.

Czech Prime Minister Mirek Topolanek, whose country currently holds the EU presidency, arrived in Ukraine on Saturday evening in an attempt to get Kiev to sign a deal aimed at ending Russia's natural gas embargo to Europe.