US STOCKS-Wall St falls but still on track for positive week
* Indexes cut gains, fall to session lows
* Ukraine engaged Russia armored column
* Monster rallies on Coca-Cola taking stake
* Indexes down: Dow 0.8 percent, S&P 0.7 percent, Nasdaq 0.6 percent (Updates to midday trading)
By Ryan Vlastelica
NEW YORK, Aug 15 (Reuters) - U.S. stocks fell on Friday, reversing earlier gains as forces in Ukraine engaged a Russian armored column on Ukrainian soil, raising the prospect of a deeper escalation in the region's unrest.
Markets had opened higher as investors continued to bet that the tension between Ukraine and Russia was waning. However, a Ukrainian military spokesman said Ukrainian forces had tracked a Russian armored column after it crossed the border into Ukraine, and that after the engagement "part of it no longer exists." Shares turned lower in heavy volume.
Investors have been concerned about the potential fallout from any escalation between the two countries, though recent signs of easing tensions had lifted equities this week.
"It is hard to know how serious this is, but any sustained upturn in violence could lead to a short-term setback," said Jim McDonald, chief investment strategist at Chicago-based Northern Trust Asset Management. Continuación...