US STOCKS-Futures point to lower open on rate hike uncertainty
* Yellen raises uncertainty about timing of rate hike
* Ukraine in view as Russia seizes naval bases
* Lennar Corp, Jabil Circuit both rise after results
* Jobless claims rise less than expected
* Futures down: Dow 39 pts, S&P 4.7 pts, Nasdaq 10.25 pts (Adds economic data, Lennar results)
By Ryan Vlastelica
NEW YORK, March 20 (Reuters) - U.S. stock index futures pointed to a modestly lower open on Thursday as investors continued to digest comments from Federal Reserve Chair Janet Yellen, who raised the specter of an earlier-than-expected rate hike.
* Yellen's comments indicated that the first increase in interest rates could come early next year, rather than in the second half of 2015, as had been widely expected by analysts. The comments ended a two-day advance on Wall Street that had taken the S&P 500 near record levels.
* Geopolitical concerns also continued to weigh on sentiment as Russian troops seized two Ukrainian naval bases, including a headquarters in the Crimean port of Sevastopol. The United States warned Russia that it was on a "dark path" to isolation in the biggest crisis between the two countries since the Cold War. Continuación...