Nationalists and other protesters clashed with police in Kyiv as demonstrators rallied in support of a blockade on coal-producing regions controlled by separatists.
Volunteer battalions last month began halting railway connections with districts in the Donetsk and Luhansk region, a move aimed at cutting off trade with regions controlled by Russia-backed fighters.
But it has also resulted coal shortages across the rest of the country and power shortages. President Petro Poroshenko last week declared a partial state of emergency that called on Ukrainians and industries to conserve electricity.
Demonstrators gathered in downtown Kyiv February 19 in support of the blockade,and some protesters later clashed with riot police.
News reports said protesters chanted "Shame on the corrupt government!" and "The enemy is within!"
Yehor Sobeliev, a member of parliament, told RFE/RL that among the seven detained by police was the leader of the Organization of Ukrainian Nationalists, Mykola Kokhanivskyi.
With reporting by RFE/RL's Russian and Ukrainian Services