MOSCOW (Reuters) - Advance units of the Syrian government army have crossed the Euphrates river and taken up position on the eastern bank, a Russian foreign ministry spokeswoman said on Friday. U.S.-backed Syrian militias opposed to President Bashar al-Assad had set the Euphrates River as a red line, saying they would not allow government forces to cross onto the east bank.   After a major victory near Deir al-Zor, the Syrian government army continues to clear Islamic State terrorists from the eastern regions of the country,  ministry spokeswoman Maria Zakharova told a news conference.  The suburbs of this provincial center have been liberated. Advance units have successfully crossed the Euphrates and are holding positions on its eastern bank.  