LONDON, July 14 (Reuters) - Chinese stocks fell back into the red on Tuesday after three days of gains, dragging broader emerging stocks lower while Iran's nuclear deal with world powers sent oil prices tumbling, taking a toll on Russian stocks and currency.
Overall, emerging assets, including in eastern Europe fell as knee-jerk gains fueled by a deal for Greece faded and the focus shifted on a deal between Tehran and six world powers that could see more Iranian crude return to world markets.
Chinese mainland stocks fell 3 percent at one stage as regulators stepped up the crackdown on unregulated, grey-market margin financing and many smaller firms resumed trading. The indexes closed around 1 percent lower.
MSCI's main emerging equity index was 0.4 percent lower, coming off one-week highs while emerging currencies broadly weakened.
In Asia, the Korean won plumbed two-year lows against the dollar and the Singapore dollar at five-week lows after data showed the economy shrinking in the second quarter due to falling exports.
Emerging European stocks and bonds were mostly weaker after the rally driven by the euro zone bailout for Greece. Bourses in Hungary and Poland slipped 0.4-0.7 percent, while the forint and the zloty weakened 0.4 percent against the euro , snapping a three-day winning streak.
"Scope for further gains in Polish zloty and its central European peers will depend on Greece's progress in approving requested bills with focus on the upcoming vote in the parliament," said Rabobank analyst Piotr Matys.
"Everything has to go very smoothly in the coming days for Greece to secure the urgently needed bailout and it all could still go wrong much sooner than the market currently anticipates."
Meanwhile Iran clinched a deal with major powers over its nuclear programme, sending crude prices 2 percent lower and taking a toll on oil exporters Russia and Saudi Arabia .
The rouble fell 0.8 percent against the dollar while dollar-denominated shares slipped more than 1 percent.
"The rouble is the weakest link against the dollar so far today as the news that Iran has reached an agreement with world powers is weighing on oil," Matys said predicting the rouble to test recent highs beyond 57.67 per dollar.
Saudi stocks - most sensitive in the Gulf to oil prices - were 0.1 percent lower, underperforming regional peers .
Lower oil added to pressure on Nigerian assets, already hurt by central bank liquidity curbs and the new president's failure to appoint a cabinet. Nigerian bank's eurobonds fell about half a cent in the dollar XS107820833=TE>
Stocks had closed Monday at the lowest in more than three months and the naira hit another record low on parallel markets.
But the oil price fall helped Turkish shares 1 percent higher for their fourth straight day of gains, while lira firmed against the greenback . Investors are also hoping that long-delayed talks on forming a coalition government will bear fruit.
For GRAPHIC on emerging market FX performance 2015, see link.reuters.com/jus35t
For GRAPHIC on MSCI emerging index performance 2015, see link.reuters.com/weh36s
For GRAPHIC on MSCI emerging Europe performance 2015, see link.reuters.com/jun28s
For GRAPHIC on MSCI frontier index performance 2015, see link.reuters.com/zyh97s
For CENTRAL EUROPE market report, see
For TURKISH market report, see
For RUSSIAN market report, see ) (Reporting by Sujata Rao and Karin Strohecker; editing by Ralph Boulton)