Leaders of the world's richest nations have called for tighter control of arms, including nuclear weapons and missiles which could be used by terrorists.
It was the first meeting for some since arguments over the Iraq war
A statement issued at the end of a Group of Eight (G8) meeting in France made specific reference to Iran and North Korea, urging them to comply with international nuclear safeguards.
The summit was the first opportunity for many of the leaders to meet since sharp divisions developed over the war in Iraq.
French President Jacques Chirac held talks with his US counterpart George W Bush, which they both said had been held in a positive and constructive atmosphere.
Huge protests which erupted into violence on the first day of the G8 meeting on Sunday were not repeated on Monday.
The closing statement from the summit in the spa town of Evian called global terrorism and the spread of weapons of mass destruction "the pre-eminent threat to international security".
It said the world community had to use weapons inspections, export controls "and, if necessary, other measures" to tackle the threat of these weapons.
"We strongly urge North Korea to visibly, verifiably and irreversibly dismantle any nuclear weapons programmes," said the statement.
It added that Iran's nuclear programme could also lead to weapons production.
A senior British official reported that Russian President Vladimir Putin had said that Moscow would "stop all nuclear exports" to Iran until it signed an additional protocol with the United Nations nuclear agency.
Russia has been helping Iran build a nuclear reactor, which US officials strongly oppose.
Earlier in the day, Iran invited the US to take part in the construction of its nuclear power plants in an effort to allay Washington's suspicions that Tehran is building nuclear weapons.
The idea was rejected last week by the US when it was suggested by Russia.
The G8 nations - Canada, France, Germany, Italy, Japan, Russia, the UK and the US - also issued an action plan designed to keep portable surface-to-air missiles out of the hands of terrorists.
The leaders discussed the 15% fall of the US dollar's value against the euro this year, but issued no statement on exchange rates.
On the economy, Mr Chirac said growth was not as strong as the G8 wanted but added: "I was struck by the real convergence of our analyses and the real conviction that all conditions exist now for a recovery."
The first meeting between the US and French presidents since they opposed each other over war in Iraq was closely watched for signs of reconciliation.
The two men appeared relaxed and said their talks had been "positive" though correspondents say the atmosphere behind the scenes remains prickly.
At their meeting, Mr Chirac told Mr Bush that he would send special forces to work alongside US troops in Afghanistan in addition to the French forces already there.
It was also agreed that Mr Chirac should visit Mr Bush in the US later this year.
Mr Bush was the first leader to leave the summit, travelling on to the Egyptian Red Sea resort of Sharm el-Sheikh for a meeting with Arab heads of state.
He said he was confident of progress when he goes on to Aqaba in Jordan for scheduled talks with the Israeli and Palestinian prime ministers on the US-led peace plan known as the roadmap.
As the summit wound down in heavily guarded Evian, a clean-up was continuing in nearby Swiss towns.
About 50,000 people gathered for a generally peaceful protest on Sunday, arguing that the world's richest nations were doing nothing to help the poorest.
But violence broke out in Geneva as masked rioters destroyed and looted shops and police used tear gas and water cannon to clear the streets.