By Menna AlaaElDin, Jonathan Saul and Kate AbnettAug 10 (Reuters) – Leaking crude oil from a tanker grounded off a nature reserve in Oman has created a slick covering almost 400 square kilometers, the country’s government said on Monday. Oman, in its first public disclosure on the environmental impact, said on Monday it was seeking to tackle the oil leak near the Hallaniyat Islands. Environmental group Greenpeace last week estimated the slick at around 600 square kilometers citing analysis of satellite imagery. It extends northeast of the islands and is within an estimated seven kilometers of the coast, the authority said. Ten years down the line, there still were remnants of oil,” he said, referring to a 1989 spill in Alaska.