Leaders of the G8 industrial nations have condemned North Korea over the sinking of a South Korean warship in March.
At a summit meeting in Toronto, Canada, the G8 - Britain, Canada, France, Germany, Italy, Japan, Russia and the United States - also criticised North Korea and Iran over their nuclear activities and described the Israeli blockade of the Gaza Strip as "not sustainable".
A communique issued at the meeting said:
"We deplore the attack on 26 March that caused the sinking of the Republic of Korea's naval vessel, the Cheonan, resulting in tragic loss of 46 lives.
"We demand that the Democratic People's Republic of Korea refrain from committing any attacks or threatening hostilities against the Republic of Korea."
The communique called on Iran to carry out a "transparent dialogue" over its nuclear programme.
The UN Security Council earlier this month approved a fourth round of sanctions against Tehran for failing to halt nuclear enrichment.
Canadian Prime Minister Stephen Harper said the world should ensure that both Iran and North Korea paid for their actions.
Canada is also hosting a summit of the G20 industrial and developing powers. The BBC reports this gathering will discuss the global economy and financial reform.
World still fragile
The statement also warned that the global recovery is still fragile.
It said the economic crisis has damaged progress toward development goals set by the United Nations for developing nations to achieve by 2015.
These include universal education and ending poverty and hunger.