Foreign ministers of the Group of Seven Most Industrialized Nations discussed ways to put pressure on Russia over conflicts in Syria and Ukraine, which have severely tarnished Moscow's ties with the West.
The United States said its priorities also included Iran's "malicious" regional activities and an end to North Korea's nuclear programs.
Western countries blame Syrian President Bashar al-Assad, who is backed by Iran and Russia, for the chemical attack that has brought Syria's seven-year conflict to the forefront of global concern. The Syrian government and its Russian ally denied the involvement or use of poisonous gas on April 7.
The foreign ministers' talks, which will conclude on Monday, will help prepare for a summit of G7 leaders in Canada in early June. The G7 includes the United States, Great Britain, Canada, Germany, France, Italy and Japan.
The group last week condemned what it said was a Russian nerve agent attack in Britain. A senior official from a G7 nation said ministers were deeply concerned about what the group saw as a model of Russia's misconduct over the years.
Russia denies any involvement in the nerve attack on British soil on 4 March.
Western nations have imposed a wide range of sanctions against Russia in recent years after the annexation of Crimea and for supporting militants operating in eastern Ukraine and for supporting Assad in Syria.
Ukrainian Foreign Minister Pavlo Klimkin took part in some of the Toronto sessions. On Saturday he held a meeting with US Undersecretary John Sullivan, during which the United States pledged its support to Kiev, but also urged him to implement economic reforms, a US representative said.
Ministers will not discuss further punitive measures against Moscow because Britain, France, Germany and Italy are members of the European Union with 28 nations, who must collectively agree on what steps to take, two diplomats briefed on the meeting said. .
The US official said the allies will also talk about developments with European partners France, Germany and Britain on updating a nuclear deal between Iran and the six great powers.
Iranian President Hassan Rouhani said on Saturday the Iranian atomic agency is ready for "expected and unexpected" reactions if the United States withdraws from the 2015 agreement signed in Vienna.
“Many of the priority issues for us today include the way forward in Syria, Iran's malicious activities in the region,” the US official said.
US President Donald Trump has called the 2015 pact with Iran one of the worst deals ever negotiated and will decide by 12 May whether to restore US economic sanctions on Tehran; this would be a severe blow to the pact.
"Our goal is to create conditions for the Vienna nuclear deal to be maintained and the United States to stay," German foreign minister Heiko Maas told reporters.
Ministers will also talk about North Korea's nuclear programs while Trump and North Korean leader Kim Jong Un prepare to meet in late May or early June. Pyongyang said on Saturday it will suspend nuclear and missile tests and will demolish its nuclear testing site.