European Union governments agreed on Tuesday to bring forward a meeting of foreign ministers expected to decide on an oil embargo on Iran by one week to January 23.
In its statement confirming the date, the EU said the decision to bring it forward from Jan. 30 was taken to avoid a scheduling clash with a summit of EU leaders set for that day.
EU states have already agreed in principle to an embargo on imports of Iranian oil, part of the latest Western efforts to increase pressure on Tehran over its nuclear program.
However, they still have to finalize details of when it will be imposed. Diplomats say the embargo could take several months to start because some EU capitals want a delay to reduce any shocks to their already sluggish economies.
EU countries have proposed "grace periods" on existing contracts of between one month and 12 months to allow them to find alternative suppliers before implementing an embargo.
Greece, which depends heavily on Iranian crude, is pushing for the longest delay, the diplomats said. Britain, France, the Netherlands and Germany wanted a maximum grace period of three months.
The goal had originally been for a final decision on Jan. 30, but the move to bring forward the foreign ministers' meeting will increase pressure for a quicker resolution.
Diplomats said an EU working group meeting on Monday had not appeared to narrow the differences and further discussions would take place this week.
European measures against Iran's oil industry will complement U.S. sanctions announced on December 31 that aim to make it impossible for most countries' refineries to buy Iranian crude.
Iran is the second largest producer of oil, after Saudi Arabia, among the 12 countries in OPEC, producing around 3.5 million barrels per day.
EU countries buy nearly 600,000 barrels per day (bpd) of Iran's 2.6 million bpd in exports, making the bloc collectively the largest market for Iranian crude, rivaling China.
The three biggest EU importers have serious debt problems. Greece imports a quarter of its oil from Iran, Italy about 13 percent and Spain nearly 10 percent.
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