U.S. Secretary of State Antony Blinken arrived in Kyiv on Tuesday to reinforce U.S. support after delays in billions of dollars of military aid forced Ukraine to ration munitions and prompted fears the U.S. would abandon its partner in the face of Russia’s invasion.

Blinken’s trip comes at an urgent time. Russia has launched a major offensive in the northeast Kharkiv region — one of its most aggressive campaigns since the invasion began in February 2022. A senior U.S. official, who spoke to reporters on condition of anonymity, said the U.S. saw the Kharkiv assault coming and has worked with Ukraine to repel it.

The top U.S. diplomat, who arrived early Tuesday after a 10-hour train trip from Poland, will highlight the battlefield gains Ukraine’s supporters say the country can make with military assistance and will showcase progress on reforms required for it to fulfill a desire for membership in the European Union and NATO.