In a statement issued at the G8 summit in St Petersburg, Russia, the group said: "We condemn the launching ... of multiple ballistic missiles on July 5 ... and express serious concerns as this jeopardises peace, stability and security in the region and beyond.
"These missile launches intensify our deep concern over (North Korea's) nuclear weapons programmes."
The leaders of Russia, the United States, Britain, France, Germany, Italy, Canada and Japan also welcomed a UN security council resolution imposing sanctions on Pyongyang that was adopted over the weekend.
On Iran, the G8 expressed "serious concern" over the country's refusal to suspend its uranium enrichment programme.
Declaring support for the right of all countries to pursue the development of nuclear energy for peaceful purposes, it stated nations should not pursue independent enrichment and fuel reprocessing programmes.
The group endorsed a plan by Moscow to establish nuclear fuel centres in Russia under UN supervision, so that countries such as Iran would be guaranteed access to fuel for power plants and would have no need for national enrichment programmes.
It also backed a US proposal to set up an international fuel bank to be overseen by the UN.
The G8 gave tacit approval to a US-India nuclear accord, yet to be approved by the US congress, that would give India access to civilian US atomic technology.
"We look forward to reinforcing our partnership with India (and) note the commitments India has made," the G8 said, adding that future nuclear co-operation with India could be possible if New Delhi took further steps on non-proliferation.