Il Nuovo Postiglione - NATO leaders gather in bid to boslter support for Ukraine

President Volodymyr Zelensky voiced hope that Tuesday's NATO summit in Vilnius would provide a "clear signal" that Kyiv could join the alliance once its war with Russia is over.

Keen to expose any hint of friction among the allies, the Kremlin fired an eve-of-summit warning that Ukraine's membership of the military alliance would have "very, very negative consequences for the entire security architecture in Europe."

On the battlefront, Ukraine's counteroffensive ground on, its forces recapturing 14 square kilometres in the past week amid "heavy fighting" near the Russian-controlled city of Bakhmut, the military said.

And Russian shelling Sunday of a humanitarian aid hub in the frontline Zaporizhzhia region killed four people, the local governor announced Monday.

- Cluster concerns -

Ahead of the summit, US President Joe Biden met with British Prime Minister Rishi Sunak during a stopover in London on Monday, with British concern over the cluster munitions deal a key subject for discussion.

Britain is one of more than 120 countries that have signed an agreement banning the production, storage, sale and use of cluster bombs, which rights groups say pose a danger to civilian populations long after they are deployed.

Biden said the decision to send the weapons was "very difficult" but Ukrainian forces were "running out of ammunition".

White House national security adviser Jake Sullivan on Sunday played down any rift between the two leaders and in NATO, saying the Biden and Sunak were "on the same page strategically on Ukraine".

China on Monday denounced the move as 'irresponsible" and said it could lead to 'humanitarian problems".

"We should fairly manage humanitarian concerns and legitimate military and security needs, and maintain a prudent and restrained attitude towards the transfer of cluster munitions," Chinese foreign ministry spokeswoman Mao Ning said.

In a summit expected to present unity on Ukraine's future membership, a key goal is to pressure Turkey to drop its opposition to Sweden's all-but-cleared membership bid.

Sweden's prime minister will meet Turkish President Recep Tayyip Erdogan on Monday afternoon in a last-gasp effort to bridge the diplomatic impasse.

Erdogan has voiced repeated frustrations with what he calls Sweden's failure to keep its promises to deal with suspected Kurdish militants allegedly "roaming the streets" of Stockholm.

He told Biden on a call Sunday that though Sweden had taken "some steps in the right direction" over Turkey's concerns, it had "nullified those steps" by allowing pro-Kurdish groups to hold demonstrations "freely praising terrorism", Erdogan's office said.

- Erdogan plays EU membership card -

And the Turkish dramatically upped the ante just hours before his meeting with Sweden's Ulf Kristersson, saying he would relent on Stockholm's candidacy if the European Union re-opened long-stalled membership talks with Ankara.

"First, open the way to Turkey's membership of the European Union, and then we will open it for Sweden, just as we had opened it for Finland," Erdogan told Turkish television before leaving for Vilnius.

Turkey formally launched membership negotiations with the bloc in 2005, but the talks stalled in 2016 over European concerns about Turkish human rights.

"Almost all the NATO members are EU members. I now am addressing these countries, which are making Turkey wait for more than 50 years, and I will address them again in Vilnius."

Turkey and Hungary remain the only NATO members still standing in the way of the unanimous ratification needed for Sweden to become the bloc's 32nd member.

Hungary has strongly signalled it will follow Erdogan's lead and approve Sweden's membership should Ankara give it the green light.

- Russian shelling hits aid hub -

On the ground, an aid hub in the town of Orikhiv in southern Ukraine was hit by Russian shelling, which killed three women and a man, regional governor Yuriy Malashko said on social media.

"They hit a humanitarian aid delivery spot in a residential area... Four people died on the spot: women aged 43, 45 and 47 and a 47-year-old man," Malashko said, calling the attack "a war crime".

Ukraine's prosecutor general said in a statement the strike had occurred one day earlier, at 1.20 pm local time (1020 GMT) and that 13 people were injured, in addition to those killed.

It released images showing a red-brick two-storey building partially collapsed and surround by debris and snapped roof beams.

E.Spicuzza--INP