* FTSEurofirst 300 down 0.8 pct, Euro STOXX 50 down 1.2 pct
* Poroshenko says Russian forces brought into Ukraine
* Mining shares drop as iron ore prices sink
PARIS, Aug 28 (Reuters) - European stocks fell on Thursday as renewed worries over turmoil in Ukraine prompted investors to cash in some gains following a sharp 2-1/2 week rally.
The sell-off accelerated around midday after Ukrainian president said Russian forces had been "brought into Ukraine".
In a statement on the presidential website, Petro Poroshenko called an urgent meeting of the Ukraine's security and defence council to decide the next steps to take in the crisis.
At 1110 GMT, the FTSEurofirst 300 index of top European shares was down 0.8 percent at 1,367.14 points. The benchmark index had surged 6.3 percent since a low hit on Aug 8.
"Geopolitics is driving the market again, and this latest escalation in Ukraine comes as European stocks were ripe for a pull-back," said Alexandre Baradez, chief market analyst at IG France.
Germany's DAX index, one of the European markets hardest hit by the Ukrainian crisis and sanctions against Moscow, tumbled 1.4 percent, with Siemens down 1.5 percent and Adidas down 1.6 percent.
According to Ukraine's security and defence council, the border town of Novoazovsk and other parts of Ukraine's south-east have fallen under the control of Russian forces who together with rebels have been staging a counter-offensive.
Russia denies intervening in Ukraine by arming the rebels or sending soldiers across the border. The defence ministry declined to comment on reports of Russian tanks in Novoazovsk.
The violence in Ukraine and tensions between the West and Russia - a major energy supplier to Europe - have muddied the forecasts of a number of multinationals including Adidas, Carlsberg, Henkel and Rheinmetall .
Around Europe on Thursday, the euro zone's blue-chip Euro STOXX 50 index was down 1.1 percent, France's CAC 40 down 0.8 percent and UK's FTSE 100 index down 0.5 percent.
Mining heavyweight Rio Tinto, Lonmin and Anglo American featured among the biggest losers, down 2.5-3.3 percent, mirroring a drop in China's iron ore futures, down nearly 3 percent on Thursday, putting spot prices on course to sink to their weakest level since 2009.
Spot iron ore prices have fallen more than 34 percent this year, as tighter credit in China has curbed purchases of imported cargoes. The rout, fuelled by excess supplies, has forced Chinese steel mills to resell some cargoes back to the market as global miners kept on ramping up output.
Bucking the trend, shares in France's Essilor climbed 4.9 percent after the world's largest maker of opthalmic lenses forecast full-year revenue growth of more than 13 percent excluding currency effects following a 7.9 percent rise in first-half sales.
Europe bourses in 2014: link.reuters.com/pap87v
Asset performance in 2014: link.reuters.com/gap87v
Today's European research round-up