Ukraine-Russia war: As Western weapons trickle through to Kyiv, Putin seizes chance to hit Kharkiv

Russia has reopened a major front in its war with Ukraine in a move that will stretch Kyiv's already undermanned and outgunned forces as they wait for Western weapons.

The Russian military unleashed a ferocious barrage of artillery and airstrikes in the early hours of Friday morning as ground troops attempted the most significant incursion into northeastern Ukraine - territory that shares a long border with Russia - in two years.

Fierce fighting raged into the weekend in different locations along a 45-mile strip of the frontier in the Kharkiv region.

Moscow claimed to have seized five villages, while Volodymyr Zelenskyy, the Ukrainian president, said battles were taking place around seven villages.

In a sign of the seriousness of the challenge, Ukraine is deploying reserve forces to help repel the Russian assault and a senior commander has been appointed to lead the effort.

The timing of the attack could not be worse for Kyiv - which presumably is why Russia decided to act.

Russian troops are already slowly gaining ground in the eastern Donbas region - a prime focus of the war - closing in on the hilltop town of Chasiv Yar.

Should that Ukrainian stronghold fall, it would give the invading troops a vantage point to strike more easily into the rest of the Donbas, putting key cities like Kramatorsk at risk.

By stepping up attacks in the Kharkiv direction, Russia could force Ukrainian commanders to divert resources from the East to the northeast, weakening their defensive line in the Donbas, which is already under huge strain.

Making the situation even more critical, delays in the delivery of additional weapons and ammunition from Western allies to the frontline have left Ukrainian forces exposed.

The United States - by far Kyiv's most important military donor - took six months to approve a $61bn (£49bn) package of assistance.

It was finally passed by Congress in April and supplies are starting to arrive.

But over the period of limbo, Ukraine's British and other European partners were unable to make up for the US shortfall because their respective militaries lack sufficiently deep stockpiles, while efforts to step up the production of new munitions are taking too long.

This is despite the urgency of a crisis that threatens security for the whole of Europe, not just Ukraine.

Rishi Sunak, the prime minister, only announced he was putting the UK defence industry on a war footing last month - more than two years after Russia launched its full-scale invasion.

In addition, Lord Cameron, the foreign secretary, told Sky News more than a week ago that Britain would be appointing an envoy to oversee the acceleration and expansion of weapons production - but that appointment has yet to be made either.

By contrast, Russian President Vladimir Putin put his entire economy on a war footing from day one. Russian production lines are delivering new supplies in defiance of western sanctions, while states such as Iran and North Korea have sold huge quantities of munitions to Moscow.

The Russian military has also benefitted from Soviet-era stockpiles of weapons that might not be particularly reliable or accurate but are better to fight with than nothing at all.

The material imbalance, coupled with Russia's ability to throw far more men into the fight than Ukraine, yet again gives the invading forces an advantage that they are exploiting.

While Mr Putin has not declared his intent, Kharkiv remains a clear target.

The regional capital was a key target of the president's full-scale invasion in February 2022.

His forces seized swathes of Kharkiv region, but never managed to conquer the city.

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A Ukrainian counteroffensive in the late summer of 2022 pushed the Russians out, but - thanks to their shared border - they never disappeared.

Instead, Russia started launching intermittent artillery and drone strikes against nearby Ukrainian villages and towns as well as longer-range missile strikes against the regional capital.

The aggression had escalated in recent weeks before erupting into Friday's ground assault.