* FTSEurofirst 300 down 0.4 pct, erases Thursday's gains
* Oil majors, miners fall as metals drop, Brent still at $78
* Nokia tumbles as margin target update disappoints
* Tensions between Russia, West also rattle investors
Prep Blaise Robinson
LONDON, Nov 14 (Reuters) - European stocks fell on Friday, erasing the previous session's meagre gains, with resource-related shares extending their recent slump sparked by a drop in commodity prices.
Telecom gear maker Nokia featured among the big losers, down 5.6 percent. Traders cited disappointment with the group's updated profit margin targets.
Renewed worries about tensions between the West and Russia over turmoil in eastern Ukraine also rattled investors after Sweden said on Friday it had proof that a small submarine was operating illegally in its waters last month.
The nationality of the craft was not identified, but the incident, which triggered the country's biggest military mobilisation since the Cold War, underlined tensions in a region increasingly worried about Russian assertiveness.
Sweden's Prime Minister Stefan Lofven said any intrusion into its territorial waters was unacceptable.
At 1230 GMT, the FTSEurofirst 300 index of top European shares was down 0.4 percent at 1,340.92 points, piercing a key support level representing its 50-day moving average.
European stocks had inched higher in early trade after data showed Germany narrowly avoided recession in the third quarter and France grew more than expected. The data, which put the euro zone on course for anaemic growth but no contraction, mitigated bearish market expectations on the bloc.
"Overall, Europe's economic environment remains sluggish, and we have to be extremely cautious in our scenario for the outlook of company results," Cholet Dupont strategist Vincent Guenzi said.
Around Europe, UK's FTSE 100 index was down 0.3 percent, Germany's DAX index was down 0.3 percent, and France's CAC 40 was down 0.1 percent.
Shares in French oil major Total were down 1.1 percent, while miners Rio Tinto and BHP Billiton both fell 1.5 percent.
Brent crude oil hovered around $78 a barrel and copper slipped again due to worries about the outlook for demand from China following weak economic data.
Europe bourses in 2014: link.reuters.com/pap87v
Asset performance in 2014: link.reuters.com/gap87v
Today's European research round-up (Editing by Sonya Hepinstall)