At least 15 people have been killed and 76 injured in a series of rocket attacks allegedly launched by pro-Russian rebels in Ukraine's port city of Mariupol on Saturday.

Ukraine’s Interior Ministry said in a statement houses in the government-held city had been hit by rockets fired by the rebels.

The Defence Ministry of the self-proclaimed Donetsk People’s Republic denied responsibility for the attacks, calling the statement “clear misinformation”.

According to Mariupol police, an open-air market in a residential area in the east of the city had been hit by rockets presumably fired from Grad multiple rocket launchers. Pro-Russian rebel forces hold positions within 10 kilometers from Mariupol's eastern outskirts.

Mariupol, one of the key cities in in the Donetsk region that remains under government control, has a population of 500,000. The city lies on the Azov Sea and is considered of strategic importance as it is sitting between mainland Russia and the Crimean Peninsula annexed by Moscow in March.

The Special Monitoring Mission to Ukraine of the Organisation for Security and Co-operation in Europe said it is looking into the circumstances of the reported artillery attack on Mariupol.

"Patrols of monitors have been sent to the shelling area in Mariupol to collect information. We will later issue an interim report on the situation," a mission spokesperson told Interfax-Ukraine.