Foreign ministers from the Group of Seven leading industrialized nations on Sunday discussed ways to pressure Russia on conflicts in Syria and Ukraine, which have badly tarnished Moscow's ties with the West.
It is the first high-level meeting of the allies since the United States, France and Britain launched 105 missiles targeting alleged chemical weapons facilities in Syria in retaliation for a suspected poison gas attack on April 7.
The United States said its priorities also included Iran's "malign" regional activities and ending North Korea's nuclear programs.
The Western countries blame Syrian President Bashar al-Assad, who is backed by Iran and Russia, for an alleged attack that thrust Syria's seven-year-old conflict into the forefront of global concern. The Syrian government and its Russian ally deny involvement or using poison gas on April 7.
The foreign ministers' talks, due to end late on Monday, will help prepare for a G7 leaders' summit in Canada in early June. The G7 comprises the United States, 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 one G7 nation said ministers were deeply worried about what the group saw as a pattern of Russia misbehavior going back years.
Russia denies any involvement in the nerve attack on British soil in March.
Western nations have imposed a wide array of sanctions against Russia in recent years after it annexed Crimea, supported militants operating in eastern Ukraine and backed Syria's Assad.
Ukrainian Foreign Minister Pavlo Klimkin took part in some of the Toronto sessions. He held a meeting with acting U.S. Secretary of State John Sullivan on Saturday during which the United States pledged its backing for Kiev but urged it to implement economic reforms, a U.S. representative said.
The ministers will not discuss further punitive measures against Moscow because Britain, France, Germany and Italy are members of the 28-nation European Union, which must agree collectively on what steps to take, said two diplomats briefed on the meeting.
The U.S. official said the allies would also discuss developments with European partners France, Germany and Britain on updating a nuclear deal between Iran and six major powers.
Iranian President Hassan Rouhani said on Saturday Iran's atomic agency was ready with "expected and unexpected" reactions if the United States pulls out of the 2015 deal, which was signed in Vienna.
"A lot of the priority topics for us today include the way forward in Syria, Iran's malign activities in the region," the U.S. official said.
U.S. President Donald Trump has called the 2015 Iran pact one of the worst agreements ever negotiated and will decide by May 12 whether to restore U.S. economic sanctions on Tehran, which would be a severe blow to the pact.
"Our aim is to create conditions so the Vienna nuclear agreement is upheld and the United States stays," German Foreign Minister Heiko Maas told reporters.
The ministers will also touch on North Korea's nuclear programs as Trump and North Korean leader Kim Jong Un prepare to meet in late May or early June. Pyongyang said on Saturday it would suspend nuclear and missile tests and scrap its nuclear test site.