Oil prices fell back Tuesday, reversing earlier gains as traders fretted over global demand worries arising from the Chinese stock market rout and a potential Greek exit from the eurozone.

In late afternoon deals, Brent North Sea crude for August delivery shed seven cents to $56.47 a barrel.

West Texas Intermediate for August dipped 50 cents to $52.03 per barrel in New York.

Analyst Jasper Lawler at trading firm CMC Markets said, “Oil demand from China could decline further if the current stock market rout spreads to the rest of the economy, while a Greek exit could affect demand for oil from Europe.”

On Monday, Brent oil had slumped $3.78 and WTI by $4.43 in highly volatile trade, as traders fretted over Greece and slowing global economic growth.

Global powers are negotiating with Iran to seal a deal curbing its nuclear programme but are not yet where they want to be.

The seven nations around the negotiating table on Tuesday admitted they would not meet a deadline for a deal and gave themselves a few more days to try to reach an accord aimed at putting a nuclear bomb out of Iran’s reach.

An agreement would put pressure on oil prices as it will lead to the West lifting crippling economic sanctions against Iran and allow Iranian oil to flow back into an already oversupplied market.