Clashes like these in Ukrainian cities are an almost regular occurrence since Russia's annexation of Crimea last month

Tensions rachet another notch as Russia puts the squeeze on Ukraine over possible gas supply cuts.

The crisis once again tops the agenda of the world's leading rich nations.

After meetings this week, US Treasury Secretary Jacob Lew warns Russia that the Group of Seven developed nations will support further sanctions if necessary.

. (SOUNDBITE) (English) U.S. TREASURY SECRETARY JACK LEW SAYING:

18:13:52 "It you look at the statements made by the chairman of the G7, by the finance minister of Germany and by myself, I think you see entire consistency. And in a discussion that went on for quite a long time in the room, there was no dissent in the room that it was essential that there be unity in taking action if necessary. Now to be clear, there was nobody in the room, myself included, who wants to be in the position where additional sanctio