* Stocks tumble in China after margin rules tightened
* Crude oil futures fall further
* Yen hits lowest since 2002 versus U.S. dollar (Adds comment, updates trading, changes dateline; previous LONDON)
By Rodrigo Campos
NEW YORK, May 28 (Reuters) - The U.S. dollar hit its highest against the yen since 2002, while global stocks cascaded lower after Chinese brokerages tightened margin rules and the IMF head downplayed talk of an imminent deal to keep Greece afloat.
Crude futures fell, with U.S. oil on track for a weekly decline following 10 weeks of gains.
A Greek government official had sparked speculation late on Wednesday that a deal to aid Athens had been drawn up. But a string of immediate denials by top European officials was followed by one from the head of the International Monetary Fund, Christine Lagarde, as G7 leaders met in Germany.
"We are all in the process of working towards a solution for Greece, and I would not say that we already have reached substantial results," she said in an interview on German television.
"Things have moved, but there is still a lot of work to do," Lagarde said, adding she believed Greece would fulfil its commitments.
Stocks were broadly lower on Wall Street, tracking declines in Europe on worries over Greece and also China, where indexes plummeted 6 percent after more brokerages tightened margin trading requirements to curb risks in a red-hot equity market.
"Greece is playing a major role in our markets at this point," said Paul Mendelsohn, chief investment strategist at Windham Financial Services in Charlotte, Vermont.
He said he expected increased volatility but "whether we are going to move in any direction or not remains to be seen."
The Dow Jones industrial average fell 56 points, or 0.31 percent, to 18,106.99, the S&P 500 lost 5.76 points, or 0.27 percent, to 2,117.72 and the Nasdaq Composite dropped 10.67 points, or 0.21 percent, to 5,095.92.
The pan-European FTSEurofirst 300 index fell 0.6 percent.
Japan's Nikkei bucked the trend, rising for a tenth session on the back of a weaker yen.
The Japanese currency touched its weakest since 2002 against the U.S. dollar, at 124.46. The euro was little changed near $1.09 and the dollar index was also steady.
"I see the dollar trade probably continuing at this point since we're the only ones moving toward a tightening bias," said Windham Financial's Mendelsohn.
"Greece is the wild card in terms of what will happen to the euro."
U.S. long-dated Treasury yields edged higher after traders took profit following a recent price rally, while data showing that U.S. weekly jobless claims unexpectedly rose drew some demand for short-dated notes.
U.S. 30-year Treasury bonds prices were last down 8/32 in price to yield 2.887 percent, from 2.875 percent late on Wednesday.
U.S. three-year notes were last up 1/32 in price to yield 0.9758 percent, from 0.989 percent late Wednesday. Benchmark 10-year notes were down 3/32 in price to yield 2.1442 percent, from late Wednesday's 2.135 percent.
Front-month Brent was down 0.5 percent at $61.78 a barrel and U.S. crude futures fell 1 percent to $56.94 per barrel.
Gold was little changed near $1,187 an ounce, spot silver was also flat on the day and copper rose 0.3 percent. (Additional reporting by the Shanghai Newsroom; Editing by Hugh Lawson and Bernadette Baum)