Ukraine and Russia targeted each other with long-range strikes, officials said Monday, amid continuing uncertainty about whether an agreement to stop their more than three-year war is within reach at the start of what America’s top diplomat called a “very critical” week.

Russia said on Monday it was waiting for a signal from Ukraine to say it was willing to hold direct negotiations to end their war, but had not seen any signs of movement.

The Trump administration has been trying to broker a peace deal between Ukraine and Russia to halt the three-year conflict.