MOSCOW, May 23 (Reuters) - Russia's biggest mobile operator MTS said on Tuesday its core profit was about 2 percent higher in the first quarter than a year ago although sales declined.
* Operating income before depreciation and amortisation (OIBDA) totalled 41.8 billion roubles ($743 million), an increase of 1.8 percent year on year;
* The growth was driven by strong mobile revenues, optimisation of costs related to roaming and a positive contribution from Ukraine;
* OIBDA margin climbed to 40.0 percent from 38.8 percent in the first quarter of 2016;
* Revenues fell 1.1 percent year on year to 104.7 billion roubles, impacted by the effect of a leap year in 2016 and as a stronger rouble limited the contribution from foreign subsidiaries where local currencies remained weak;
* Net income was down 14 percent to 12.5 billion roubles from 14.5 billion roubles in Q1 2016 due to a smaller foreign exchange gain and higher depreciation and amortisation costs related to network expansion;
* Free cash flow was 11.4 percent higher at 22.9 billion roubles;
* MTS confirmed its full-year 2017 outlook for revenue and adjusted OIBDA growth rate at +2 pct/-2 pct;
* "We may be trending at the upper range of this guidance, but the macroeconomic situation, including currencies throughout our markets, remains volatile," MTS Chief Executive Officer Andrei Dubovskov said.
* "The competitive outlook despite steps we took during the period to shut down stores and eliminate unlimited tariff plans remains uncertain. Overall, however, we see a number of positive underlying trends in our market," he added.
* Rosneft's lawsuit against MTS' parent company Sistema has no impact on MTS' operational activity, strategy or dividend payments, Dubovskov and MTS Chief Financial Officer Alexei Kornya told reporters.
* State-controlled oil firm Rosneft filed a lawsuit this month seeking more than 100 billion roubles from Sistema over assets Rosneft says had been removed from oil company Bashneft in which Rosneft bought a controlling stake last year. Further company coverage: ($1 = 56.2750 roubles) (Reporting by Anastasia Teterevleva; writing by Maria Kiselyova; editing by Dmitry Solovyov)