Leaders of the Group of Eight (G8) industrialised nations have condemned North Korea over the sinking of a South Korean warship.
The G8 - the US, Canada, Germany, UK, France, Italy, Russia and Japan - also criticised of North Korea and Iran over their nuclear activities at their summit in Canada.
And they described the Israeli blockade of the Gaza Strip as "not sustainable".
Canada is also hosting a summit of the G20 industrial and developing powers.
This gathering will discuss the global economy and financial reform.
A communique from the G8 said: "We deplore the attack on March 26 that caused the sinking of the Republic of Korea's naval vessel, the Cheonan, resulting in tragic loss of 46 lives."
Noting that an international investigation had found that, despite its denials, Pyongyang was to blame for the attack that sank the corvette, the statement added: "We condemn, in this context, the attack which led to the sinking of the Cheonan.
"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 controversial nuclear programme.
The UN Security Council earlier this month approved a fourth round of sanctions against Tehran for failing to halt nuclear enrichment.
The measures include tighter finance curbs and an expanded arms embargo, but not the crippling sanctions the US had wanted.
Later the EU imposed additional sanctions against Iran - a moved that was criticised by Russia.
'Dilemma'
Efforts to bridge differences over budget policy dominated Friday's talks before Saturday's discussions on global security.
The twin summits, being held in and near Toronto, have come at a time when largest economies are divided over whether to cut deficits or stimulate economic growth.
US President Barack Obama is worried that a series of austerity measures announced by European countries may delay global recovery.
The G8 leaders will soon be joined by China and other rising economic powers for the G20 summit.
Mr Obama has called for the group to pull together to promote economic growth, saying that world economies are "inextricably linked".
BBC economics correspondent Andrew Walker says there is a dilemma for the group on the best timing for fixing debt problems.
Also on Friday, the G8 also agreed to donate $5bn (£3.3bn) over five years towards improving the health of mothers and young children in the developing world.
The pledge, intended to help tackle one of the UN Millennium Developments goals, was described as inadequate by anti-poverty groups.
