The quake centered on the Iranian city of Khoy and affected villages in the Turkish province of Van.
Soylu told a news conference in Ankara that three children and four adults were killed in Turkey's Baskule district. Five injured people had been taken to hospital while others remained trapped under the debris of fallen buildings, he added.
Emergency teams have been sent to the mountainous region.
Iran's official IRNA news agency said the earthquake affected 43 villages in the mountainous Qotour area. It report some residents were injured but didn't say any were in critical condition.
According to the European Mediterranean Seismological Center the quake had a depth of 5 kilometers (3 miles).
The region has a history of powerful earthquakes. Last month a quake centred on the eastern Turkish city of Elazig killed more than 40 people.