Oil prices dropped on Monday, tracking a sell-off in global equity markets and the euro caused by fears of a Greek debt default, analysts said.

US benchmark West Texas Intermediate for August delivery slid $1.40 to $58.23 compared with Friday's close.

Brent North Sea crude for August lost $1.71 to stand at $61.55 a barrel in London midday trade.

Daniel Ang, investment analyst at Phillip Futures, said the weakening euro "could see crude prices continue to drop, similar to what we have seen at market open".

A more expensive US currency makes dollar-priced crude more expensive for buyers holding the European single currency, denting demand.

Elsewhere, dealers are waiting to see if Iran and major world powers can reach a deal on curbing Tehran's nuclear programme by the end of the month.

Such a move would allow Western powers to remove sanctions, paving the way for more Iranian crude to hit the already oversupplied international market.

A senior US official at the talks in Vienna would not say there was no chance of nailing down the accord by Tuesday, but admitted "it's fair to say the parties are planning to stay past (June 30th) to keep negotiating".

Iran has the world's fourth-largest oil reserves but its exports have fallen from more than 2.2 million barrels per day in 2011 to about 1.3 million because of the sanctions.