LISBON, Feb. 27 (Xinhua) -- The Portuguese government is to establish a working group to combat illegal overland fuel imports from its neighboring country Spain, the finance ministry said Monday in a statement.

The aim of the working group is to "defend competition and the supervising and monitoring of economic activities," said the statement published in the official daily Diario da Republica.

The group will investigate the "irregular entry of fuel into the national territory with a special focus on road fuel, diesel and petrol."

The issue revolves around the price differential between fuel bought in Portugal and Spain. Taxes levied on diesel and petrol in Spain are considerably lower than those in Portugal. Big profits can therefore be made by buying fuel in Spain and importing it undeclared for sale in Portugal.

The new working group will include members of the government's Energy and Fiscal Affairs departments, as well as officials from the National Entity for the Fuel Market, Portugal's Tax and Customs authority and the Food and Economic Security Authority.

The group has until July 31 to present its findings and recommendations.

In January, Portugal issued summons to five companies involved in importing fuel by land, claiming 48 million euros (59.22 million U.S. dollars) in lost revenue.

In October 2017, the Portuguese Association of Petroleum Companies (Apetro) told the Lusa Portuguese News Agency that it suspected a quarter of all fuel imported by land from Spain is undeclared.