BP PLC will likely have to shut down a natural gas field in the North Sea that it jointly owns with Iran, a sign that tough new European sanctions are beginning to affect the Islamic Republic's oil and gas sector.

European Union foreign ministers approved new measures Monday which would, among other things, ban joint energy investments by Iranian and Western companies.

The sanctions are designed to bring Iran to the negotiating table over its nuclear program.

A spokesman for the EU foreign-affairs chief Catherine Ashton said the new sanctions would affect Rhum, a gas field co-owned by BP and a state-owned Iranian oil company, "and could lead to its closure."

In and of itself, the shutdown of Rhum would have few repercussions for BP, the U.K., or Iran. It is a small field, producing the equivalent of 15,000 barrels of oil a day, and accounts for just 5% of BP's U.K. North Sea oil and gas production, the company says. EU officials say it is the only Western-Iranian joint venture of its kind in Europe.