NEW DELHI: US Secretary of State Antony Blinken on Tuesday morning  made an unannounced visit to Ukraine to reassure the continuous support of the United States to Kyiv as well as the supply of weapons as Russia continues to attack the northeastern Kharkiv region.

He is on his fourth visit to Kyiv since Russia invaded Ukraine in February 2022. Blinken took an overnight train from Poland and was supposed to hold talks with Ukrainian President Volodymyr Zelensky.

Blinken is visiting Ukraine weeks after a financial aid package worth $61 billion was approved by the US Congress for Ukraine after months of delay. The package unlocked much-needed arms for the stretched troops of the country.

It is expected that the aid will be provided at an accelerated pace as Washington is trying to make up for the lost months, even though Congress is facing difficulty in reaching a complete agreement on assistance.

"First this trip is to send a strong signal of reassurance to the Ukrainians who are obviously in a very difficult moment both with grinding battle on the Eastern Front but also with the Russians now expanding some cross-border attacks into Kharkiv," said a senior US official, while speaking to the reporters aboard the train.

Antony Blinken is expected to look into how US aid will "be executed in a fashion to help shore up their defences and enable them to increasingly take back the initiative on the battlefield."

The senior US official had last visited in March when National Security Advisor Jake Sullivan reached Ukraine.

Russia is "clearly throwing everything they have in the east and expanding the fighting to Kharkiv is representative of that strategy," said the official.

"But we have a lot of confidence that the Ukrainians will increasingly be effective in pushing the Russians back as our assistance flows in both from the United States and other allies and partners," he added. 

Alongside holding discussions with Zelensky, Blinken is likely to meet his counterpart Dmytro Kuleba along with members of civil society and deliver a speech on the topic "Ukraine's strategic success".

The secretary of state will also discuss a bilateral defence agreement which the United States hopes to close before the NATO summit in Washington in July.

"The negotiations are in their final stages, we're very close," the US official said.