Iranian crude oil tankers are still restricted by international sanctions because of problems with insurance coverage, an official said Monday.

Ali Akbar Safaei, director of the National Iranian Tanker Co., said that, although sanctions in the company were lifted, getting insurance coverage was still restricted by international sanctions.

Iran last year secured modest relief from sanctions targeting its energy sector in exchange for agreement to curb some of its nuclear research activity.

U.S. Secretary of State John Kerry traveled Monday to Vienna to meet with Iranian Foreign Minister Javad Zarif and European delegates leading multilateral nuclear negotiations. The U.S. State Department said Kerry is expected to weigh Iran's willingness to make the "critical choices" necessary for a comprehensive agreement on nuclear issues.

Safaei last week said his company should make a strong recovery following a recent ruling from the European courts last week that it made a "manifest error" when imposing sanctions on certain Iranian entities tied to the nuclear sector.

Safaei said the ruling means EU sanctions against NITC are annulled.

NITC transports Iranian crude oil to export markets and is responsible for the distribution of oil products to Iranian ports.