KYIV, Ukraine, May 14, 2024 (BSS/AFP) - American military aid for Ukraine is "on its way", US Secretary of State Antony Blinken said in Kyiv on Tuesday, as Russia pressed on with a new offensive in the northeastern Kharkiv region.

Blinken's trip comes just weeks after the US Congress finally approved a $61 billion financial aid package for Ukraine after months of political wrangling, unlocking much-needed arms for the country's stretched troops.

"In the near term, assistance is now on its way that and that will make a real difference against the Russian aggression," he told Ukrainian President Volodymyr Zelensky.

Blinken arrived by overnight train from Poland on his fourth visit to Kyiv since the start of the Russian invasion in February 2022.

Zelensky thanked Washington for the aid, saying: "The decision on the package was crucial for us".

He said the biggest deficit for Ukraine was air defence and asked for two Patriot batteries in the Kharkiv region, where Russian forces have been advancing and pounding villages along the border.

At a checkpoint outside the city of Kharkiv, an official said Russian forces had entered Ukraine through "villages on the very border which were complicated for us to defend".

"They are on high ground and are shelling us from there," said the official, Volodymyr Usov, head of the Kharkiv district military administration.

The White House said Monday it was doing "everything" possible to rush weapons to Ukraine.

US National Security Advisor Jake Sullivan told reporters a new arms package would be announced "in the coming days."

- 'Intense enemy fire' -

The surprise Russian ground offensive in the Kharkiv region, which began on Friday, has forced thousands to evacuate and pushed Kyiv to mobilise reinforcements.

The Ukrainian army acknowledged Russia was "achieving tactical success" but Zelensky stressed Kyiv had sent reinforcements to Kharkiv and that "our counterattacks are ongoing".

"We are getting more and more results, destroying the occupier's infantry and machinery," he said in a Monday evening address.

"Our task is crystal clear: to thwart Russia's attempt to expand the war".

Zelensky said Kyiv had also noted strikes and "hostile activity" targeted against the Sumy and Chernihiv regions in northern Ukraine.

In the east of the country, where several areas had been subject to "intense enemy fire", Ukrainian forces had changed their positions "to save the lives of our defenders" and were planning to regroup units, the army said late Monday.

Ukraine's security council chief Oleksandr Lytvynenko said Moscow had massively upped its troop deployment for the new offensive in the Kharkiv region.

"There are a lot of Russians, quite a lot. About 50,000 were on the border. Now there are much more than 30,000 coming," he told AFP on Monday.

However, he said "we don't see any threat of assault on the city of Kharkiv", around 30 kilometres (20 miles) from the combat zone.

Russia's defence ministry said its troops had "improved the tactical position and dealt a blow to (Ukrainian) manpower" around border villages, including Lyptsi, and the town of Vovchansk.

- Bombs falling 'like rain' -

Kateryna Stepanova, 74, who fled Lyptsi with her son, said several bombs had hit her street.

"We weren't going to leave... but now this. Thankfully, we're alive," she said, sitting in a minibus at a gathering point for evacuees.

"They are shelling the villages, firing everything they can," Sergiy Kryvetchenko, deputy head of the Ukrainian military administration in Lyptsi, told AFP.

Guided aerial bombs are falling "like rain" said one serviceman, who was resting after fending off Russian assaults in Lyptsi.

An overnight strike on Kharkiv wounded two people, regional governor Oleg Synegubov said Tuesday on Telegram.

In Russia, the defence ministry said air defences had intercepted 25 Ukrainian rockets in the Belgorod region.

Elsewhere, in the Volgograd region, freight train carriages were derailed in Kotluban station due to the "intervention of unauthorised persons," Russian news agencies said Tuesday.

No details were given about the incident or who caused it.

Kyiv did not claim responsibility but a Ukrainian advisor to the mayor of Mariupol, which was seized by Russia in spring 2022, called it "good news".

According to him, the station had a branch line "leading to the arsenal of the main missile and artillery department of the (Russian) ministry of defence".

Kotluban is about 300 kilometres from the border with Ukraine, and the Volgograd region is sometimes the target of drone attacks launched by the Ukrainian army.