On Thursday evening, Russian drones assaulted the Ukrainian capital Kyiv, the fourth strike in as many days, causing inhabitants to hear gunshots and explosions, and at least one drone was shot down.

Kyiv and the surrounding region had been pronounced safe by city officials. Residents who went to air raid shelters reported that the drones came faster than normal after the alarms were issued. Reuters witnesses reported hearing gunshots and larger blasts near the city center.

The attacks started just after 8 p.m. (1700 GMT) and lasted around 20 minutes. Ukraine’s air force said in a statement that it had destroyed one of its own drones after the drone lost control over Kyiv region, probably because of a technical failure. It wasn’t clear how many drones in total were destroyed.

Russia said on Thursday that the United States was behind a purported drone attack on the Kremlin aiming to kill President Vladimir Putin. Washington and Kyiv denied involvement.

Putin will head a scheduled meeting of Russia’s Security Council on Friday and the Kremlin incident could be on the agenda, TASS news agency reported.

Ukrainian President Volodymyr Zelenskiy, speaking in The Hague after visiting the International Court of Justice, said Putin must be brought to justice over the war and that Kyiv would work to create a new tribunal for this purpose.

In other diplomacy, U.S. Ambassador to the United Nations Linda Thomas-Greenfield said on a visit to Brazil that she encouraged the government to include Ukraine in any attempt to negotiate an end to the war. She was referring to President Luiz Inacio Lula da Silva’s comments calling on the West to stop arming Ukraine to allow peace talks to start.

There are currently no peace talks to end the war, which has devastated Ukrainian towns and cities, killed thousands of people and driven millions from their homes.