Prime Minister Dmitry Medvedevhas signed a decree banning Russian exports of coal, crude oil and oil products to Ukraine, he told government officials in televised comments on Thursday. Starting June 1, the export of products listed in the decree will require an individual permit, Interfax reported. Russian authorities are also considering an expansion of a ban on importing certain Ukrainian goods in response to “unfriendly” actions by Ukraine, he added. “The Ukrainian Cabinet of Ministers took another unfriendly step towards our country, expanding the list of Russian goods prohibited for import into Ukraine. Under these conditions, we have to defend our interests and take retaliatory measures,” Medvedev was quoted as saying by Interfax. Ukraine is preparing to hold the second round of its presidential election this Sunday and relations with Russia are a key campaign subject. This story is being updated. Reuters contributed reporting to this article.