(Recasts with G7 set to maintain tough language on Russia)
TORONTO, April 22 (Reuters) - Foreign ministers from the Group of Seven leading industrialized nations are expected to maintain a tough line on Russia over its involvement in conflicts in Syria and Ukraine, while leaving the door open to cooperation, two sources briefed on the matter said on Sunday.
The ministers, meeting in Toronto for two days, spent part of the first day discussing tensions with Russia, which are straining an already bruised relationship with the West.
The sources, speaking on condition of anonymity, said a final statement from the ministers was set to maintain an uncompromising line with Moscow, which the G7 has condemned for annexing Crimea and backing militants in eastern Ukraine.
"The language will be tough because of what the Russians have done until now. But it can also be interpreted as leaving the door open," said one sources, who requested anonymity because they were not authorized to speak to the media.
"We are saying to them, 'If you want to be treated as a great power, then work with us'," the source said.
German Foreign Minister Heiko Maas called on Moscow to help resolve the crisis in Syria, where Russia and Iran are backing Syrian President Bashar al-Assad.
"We know that the Syrian conflict, for example, can't be solved without Russia. But it must then come up with constructive offers in return," he told reporters on Sunday.
The G7 meeting is the first high-level gathering of the allies since the United States, France and Britain launched 105 missiles targeting chemical weapons facilities in Syria in retaliation for a suspected poison gas attack on April 7.
The Western countries blame Assad for the attack that killed dozens of people. The Syrian government and its Russian ally deny involvement or using poison gas on April 7.
The United States said its priorities also included Iran's "malign" regional activities and ending North Korea's nuclear programs.
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 G7 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.
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 meetings are not expected to 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 issue could, however, be raised in bilateral talks among the G7 members, one official added.
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 agreement, which was signed in Vienna.
"One of the things we are concerned about now is the (deal) and where that is headed," British Foreign Secretary Boris Johnson told Sullivan on the sidelines of the G7 meeting.
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.
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.
(Additional reporting by Sabine Siebold in Toronto; Editing by Meredith Mazzilli, Lisa Shumaker and Cynthia Osterman)