Secretary of State John Kerry is heading to Moscow for talks on Ukraine and Syria as Tuesday's terrorist attacks in Brussels underscored the urgency of fighting the Islamic State group.

In talks with Russian President Vladimir Putin and Foreign Minister Sergey Lavrov on Thursday, Kerry is to discuss the fragile truce in Syria that the U.S. hopes will spark UN-brokered peace talks amid disagreements over how to verify and respond to alleged violations, the State Department said.

Kerry will also call on Russia to do more to press pro-Russian separatists to comply with a ceasefire in eastern Ukraine. He is expected to raise the case of Nadezhda Savchenko, a Ukrainian pilot who was sentenced to 22 years in prison in Russia on Tuesday on charges the U.S. says are false.