U.S. envoys Steve Witkoff and Jared Kushner arrived in Moscow on Saturday to try to revive a stalled push to end Russia’s full-scale invasion of Ukraine, Russian state news outlets reported.

The visit came as both sides escalated their aerial attacks. Ukrainian President Volodymyr Zelenskyy said that Ukraine would halt airstrikes during the envoys’ trip and urged Moscow to do the same. Moscow did not publicly respond to the proposal.

Washington’s push to end the fighting, now in its fifth year, has lost momentum as U.S. attention has been focused for the last six months on its war with Iran.

The envoys were met at the airport by Russian envoy Kirill Dmitriev, Russia’s state news agency Tass said.

The last known visit to Moscow by Witkoff and Kushner, U.S. President Donald Trump’s son-in-law, was in January, when they met Russian President Vladimir Putin in the Kremlin. They have never visited Kyiv, but Zelenskyy said he was expecting them in the Ukrainian capital on Sunday.

With peace efforts stalled, Russia intensified its attacks on Kyiv and other cities with relentless bombardments recently stretching into daylight hours, taking advantage of Ukraine’s shortage of air defensive systems.

On Friday, a Russian drone hit one of the most important government buildings in Kyiv — the headquarters of Ukraine’s Security Service, known as the SBU, which is one of the agencies involved in carrying out deep-strike operations inside Russia.

The long-range strikes by Ukraine have hit Russian military facilities, oil refineries and e-commerce hubs, seeking to undermine the Kremlin’s war effort and economy, as well as make ordinary citizens feel the consequences of the war.

Zelenskyy links Russian strikes to envoys’ visit

The air war between Russia and Ukraine has intensified as troops have struggled to make progress along the 1,250-kilometer (775-mile) front line. Russia has recently been using fast-flying, jet-powered drones, and the recurring wail of air-raid sirens has become part of daily life in Kyiv.