BRUSSELS (Reuters)—European Union diplomats have postponed a decision on whether to grant exemptions to a ban on insuring Iran's oil shipments, which is being introduced as part of sanctions against the country but has drawn fire from Asian oil importers.

"For the moment there is no deal," an E.U. diplomat with close knowledge of the talks said on Tuesday.

"Discussions will continue tomorrow," the diplomat said, adding negotiators hoped to reach an accord before a meeting of E.U. foreign ministers scheduled for Friday.

The E.U. agreed to an oil embargo in January to stop members from importing crude from Iran as part of sanctions aimed at isolating the country over its suspected nuclear weapons program.

The strategy includes a ban on E.U. insurers and reinsurers from indemnifying vessels carrying Iranian crude and fuel anywhere in the world.

That could prevent Iran's biggest crude buyers in Asia from importing Iranian crude because they rely on European insurers who cover most of the world's oil tanker fleet.

Japan and South Korea have lobbied European governments for exceptions to ensure oil deliveries.

Some E.U. countries, however, are wary of weakening the impact of E.U. measures on Iran, particularly as member states such as Greece are making big sacrifices, such as giving up favorable deals with Iran, as part of the sanctions.

"To tell Greece that we are going to exempt insurance to Japan means we agree that Japan can go on buying oil," said one senior E.U. official. "So for countries in Europe that are making a lot of sacrifices, it is not easy to understand why you have a special treatment for someone and not for them."

The E.U.'s January decision included a transition period that allows E.U. states to continue bringing in oil to Europe under existing contracts until July.

On Tuesday, representatives in Brussels of E.U. governments debated a proposal to allow all insurance on Iranian crude bound for countries outside the E.U. to be extended until July 1.

Rising international political tension between the West and Iran and uncertainty over how the E.U. embargo and U.S. sanctions will impact oil supplies have driven up benchmark crude prices. So Iran is receiving a higher price for its exports, while importers such as Japan and South Korea face a rising fuel bill.

Tehran denies Western charges over its nuclear program, saying it is for peaceful purposes such as power generation.