US Secretary of State Antony Blinken has arrived in Kyiv on an unannounced diplomatic mission to reassure Ukraine it has American support as it struggles to defend against increasingly intense Russian attacks.

The visit comes less than a month after Congress approved a long-delayed foreign assistance package that sets aside 60 billion dollars (£48 billion) in aid for Ukraine.

Much of the aid will go toward replenishing badly depleted artillery and air defence systems.

US officials said that on his fourth trip to Kyiv since Russia invaded Ukraine in February 2022, Mr Blinken will underscore the Biden administration’s commitment to Ukraine’s defence and long-term security.

They noted that since President Joe Biden signed the aid package late last month, the administration has already announced 1.4 billion dollars (£1.1 billion) in short-term military assistance and six billion dollars (£4.7 billion) in longer-term support.

It is “trying to really accelerate the tempo” of US weapon shipments to Ukraine, national security adviser Jake Sullivan said.

“What I am going to suggest is that the level of intensity being exhibited right now in terms of moving stuff is at a 10 out of 10,” Mr Sullivan told reporters at a White House briefing on Monday.

Artillery, air defence interceptors and long-range ballistic missiles have already been delivered, some to the front lines, said a senior US official travelling with the secretary on an overnight train from Poland.

The official said Mr Blinken will “send a strong signal of reassurance” to Ukrainian leaders and civil society figures he will meet during his two-day visit.

In a statement released after Mr Blinken’s arrival, the State Department said he would meet with President Volodymyr Zelensky and other top Ukrainian officials “to discuss battlefield updates, the impact of new US security and economic assistance, long-term security and other commitments, and ongoing work to bolster Ukraine’s economic recovery”.

Delays in US assistance, particularly since Israel’s war with Hamas began to preoccupy top administration officials, triggered deep concerns in Kyiv and Europe. Blinken, for example, has visited the Middle East seven times since the Gaza conflict began in October.

His last trip to Kyiv was in September.

The US official added that Mr Blinken would give a speech on Tuesday extolling Ukraine’s “strategic successes” in the war.

It is intended to complement an address last year in Helsinki, Finland, in which he derided Russian President Vladimir Putin for Moscow’s strategic failures in launching the war.