Russian President Vladimir Putin and North Korea's leader Kim Jong Un have vowed to strengthen cooperation, days ahead of Putin's summit in Alaska with Donald Trump, Pyongyang's state media reported Wednesday.

Kim Jong Un provides Moscow with artillery, missiles - and as a BBC investigation shows, labourers working in 'slave-like' condition.

Russian president Vladimir Putin, in a letter to North Korean leader Kim Jong Un, thanked North Korea for its support and assistance in the war against Ukraine, calling the cooperation between the countries a strategic partnership,