* Auto stocks down as JP Morgan cuts China market forecasts
* Oil prices fall after Iran nuclear deal
* Gjensidige, Kuehne & Nagel rise after earnings
* European bourses in 2015: link.reuters.com/pap87v
* Asset performance in 2015: link.reuters.com/gap87v
By Sudip Kar-Gupta
LONDON, July 14 (Reuters) - European stocks slipped back on Tuesday after a four-day rally, as carmakers fell on concerns about the Chinese market and a landmark nuclear deal on Iran undercut oil prices and energy stocks.
The deal between Iran and six global powers is set to ease sanctions against Tehran and allow a gradual rise in its oil exports, weighing further on already weak oil prices. The STOXX 600 Europe Oil & Gas Index weakened by 0.2 percent.
Carmakers also fell as JP Morgan cut its forecasts for the Chinese auto market, a day after Brilliance China Automotive Holdings, which makes BMW cars in China, issued a profit warning.
JP Morgan also cut its price target on Volkswagen. Volkswagen slid 3.6 percent to make it the worst-performing stock in percentage terms on the pan-European FTSEurofirst 300 index, which was down 0.1 percent.
"We remain a seller of German car stocks, especially BMW," said Gary Paulin, co-founder of brokerage Aviate Global.
The FTSEurofirst had gained about 9 percent over the last week on hopes of a Greek debt deal.
However, just hours after Greek Prime Minister Alexis Tsipras signed up for austerity in return for talks on an 86 billion euro ($95 billion) bailout, doubts were already emerging about whether he could hold his government together.
The euro zone's Euro STOXX 50 index slipped 0.4 percent after hitting a two-week high on Monday, while German utility RWE retreated 2.2 percent after UBS downgraded RWE to "sell" from "neutral".
Among stocks gaining ground, Norwegian insurer Gjensidige rose 1.8 percent after its earnings beat expectations, while Switzerland's Kuehne und Nagel also climbed on the back of a rise in its earnings.
The FTSEurofirst 300 is up about 15 percent since the start of 2015, with the Euro STOXX 50 up 14 percent.
Today's European research round-up ($1 = 0.9059 euros) (Additional reporting by Alistair Smout; Editing by Louise Ireland/Ruth Pitchford)