The Latest on Syria's complex civil war (all times local):

8 p.m.

Russia's Foreign Ministry says U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov have stressed the need for more cooperation between their two countries to strengthen the cease-fire in Syria.

The ministry statement said that during Sunday's phone conversation, Lavrov and Kerry also discussed efforts to fight the Islamic State group, the al-Qaida-affiliated Nusra Front and other terrorist organizations, agreeing to take additional measures to halt the flow of militants and weapons from abroad.

Lavrov's office also said the two diplomats expressed support for the efforts of the U.N. envoy to Syria, Staffan de Mistura, to convene the next round of talks in Geneva between the Syrian government and the opposition.

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7:30 p.m.

Activists say airstrikes around the Syrian city of Raqqa, the de facto capital of the Islamic State group, have killed several civilians and militants.

The Syrian Observatory for Human Rights says the airstrikes on Sunday killed three IS leaders and 21 other militants as well as eight civilians.

Raqqa Is Being Slaughtered Silently, a group of activists with contacts inside the city, says a prominent IS judge was among those killed.

It says Fawaz al-Hassan, also known as Abu Ali al-Shari, had been kicked out of IS over his extreme legal interpretations, but was later brought back into the fold to frighten potential defectors. It says 20 civilians were killed in the strikes.

Russia, Syria, and a U.S.-led international coalition have been bombing IS territory for months. It was unclear who was behind Sunday's strikes.

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4:15 p.m.

Syrian activists say the Islamic State group has launched a major offensive along the Turkish border, seizing two villages near a border town captured by Western-backed rebels two days ago.

The Britain-based Syrian Observatory for Human Rights, which relies on activists inside the country, says IS militants seized Sheikh Reeh and al-Bal on Sunday.

The activist-run Azaz Media Center, based in a northern town of the same name, says the extremists exploded seven bombs around Marea and other villages and towns, calling it the fiercest IS offensive in a year.

The IS-linked Aamaq News Agency claims the capture of the two villages and says a suicide operation targeted rebel fighters in opposition-held Kafr Shousha.

The Western-backed Free Syrian Army captured the border town of al-Rai from IS on Friday.