Whenever the wind blows northwest from Belarus, Lithuania braces for problems.

That's when giant white balloons are launched across the border, crates of cheap cigarettes dangling beneath.

Over the past 10 weeks, the illicit balloon traffic has already forced Lithuania's main airport into shutdown 15 times, stranding or delaying thousands of travellers.

On one occasion the airspace was closed completely for 11 hours.

But the government here is sure it is dealing with something far more hostile than smugglers.

It says the balloons have been weaponised in an act of hybrid warfare by Belarus, Russia's closest ally. It is happening just as Moscow's own shadow war on Europe is escalating again with a wave of arson and sabotage attacks that officials link to Russian intelligence.

Emergency response

The Lithuanian government has declared an emergency situation.

Balloons have been used by smugglers before, but this October their number suddenly surged.

Of course it started as organised crime activity across the border, but we've seen more than once how Belarus instrumentalises organised crime to have an effect on neighbouring countries, Foreign Minister Kestutis Budrys told the BBC in the capital Vilnius.

He says the balloons are launched from spots that help them best target Lithuania's main airport, just 30km (19 miles) from the border.

If you want to make a smuggling operation to take a couple of thousand packs of cigarettes to the other side, you'd do it in the woods or the swamps, not directly at our airport! the minister argues.

Instead, he believes the balloons are a form of political blackmail on Europe's eastern edge.

[Belarus] sees this as leverage: 'You have a border with us, we can cause you huge problems', Budrys says. What they're doing is really touching the military and security field and we want to prevent a military escalation.

Now every night the military police head out on patrol in the border zone. The balloons are most common after dark.

Rattling across fields to reach remote country roads, they then set up mobile checkpoints and step out to stop vehicles at random. They check the drivers' documents and search car boots looking for anyone who may be involved in the smuggling, in the hope of smashing the networks.

The balloons fly too high to make shooting them down with air defences a safe or economic option, so the government has offered a €1m (£870,000) prize to any firm that can figure out how to intercept them.

In the meantime, teams use military radar to track the balloons in the sky and try to catch smugglers who turn up where the cargo drops.

What is Belarus up to?

The border itself is now marked by a tall metal fence, with a coil of vicious-looking barbed wire on top and more beyond. Below are giant concrete blocks marking the line before a Belarusian flag and a border post.

All this extra security is the most obvious sign of how Lithuania now views its neighbour - and its ally Russia - as hostile and dangerous.

Not far away in Minsk, the man who has ruled Belarus for three decades, Alexander Lukashenko, dismisses all the talk of hybrid warfare as nonsense.

He recently blamed bandit smugglers for the balloons, saying they were just seeking a profit and getting creative about overcoming the new security fence.

Lithuania doesn't buy that, partly because Belarus already has form when it comes to hybrid attacks on the border. In 2021 migrants trying to reach the EU were helped to cross into Lithuania and Poland in big numbers, provoking a deliberate crisis.

But there are other signs of state involvement.

In Vilnius, Vilmantas Vitkauskas runs the crisis management centre that brings together various branches of government and security services.

Before, he says, smugglers would send their balloons in clusters to overwhelm security forces on the other side. Now they are doing a sequence of one or two balloons every 30 minutes, aimed directly at the airport, he explains in front of a giant digital wall map that charts all the balloons spotted so far this year.

In Lukashenko's Belarus... if they were interested in stopping it they can do it tomorrow. But they don't. That means it benefits them.

The suspicion is that Belarus is trying to bully its way into reducing sanctions.

They want to attract political attention and force us to change our policies towards Belarus, is how minister Kestutis Budrys sees the sudden influx of balloons.

The EU doesn't recognise Alexander Lukashenko as president because he imprisoned his main opponents ahead of disputed elections in 2020 and oversaw a brutal crackdown afterwards. The sanctions that were imposed then were tightened two years later when he helped Vladimir Putin launch Russia's full-scale invasion of Ukraine.

First, they want to end the international isolation of the regime and number two, of course, the sanctions, the minister argues.

The US has just agreed to lift some sanctions on Belarus, with the country afterwards freeing 123 prisoners, including prominent opposition activist Maria Kolesnikova.

But Budrys argues for a harder line with Minsk from Europe. We have to expand the sanctions regime against Belarus to include hybrid activities against the EU, he says.

Disruption and delays

For now, travellers to and from Lithuania – and the airlines – are having to adapt.

This is something completely new for the aviation sector, none of the airports in Europe experienced that, airport CEO Simonas Bartkus says, inside a shiny new terminal in Vilnius.

One airline has already relocated its charter flights to Lithuania's second city and another has cut its evening flight service to Vilnius.

Mr Bartkus estimates the loss of revenue for all affected businesses will reach €2m by the end of the year. One thing is the extra cost for us and the airlines, but the even higher risk is if passengers start to lose trust in air travel, he admits.

Already, travellers check a new webpage that gives the wind forecast and the likelihood of balloons floating into their flight path before booking.

It's not easy, it makes me a little bit nervous. I'd just like to get home as planned, a Polish passenger said, as he waited in the terminal.

For the last week we were checking every day, a local woman, Justina, said.

We believe this is a hybrid attack on us. I think for them it's really funny to fly those balloons and then laugh at us, not dealing with it.

Her words hint that another aim of hybrid activity attacks - sowing discontent and political division - is also working, and perhaps harder to defend against.

They're basically testing the limits of Nato: looking how we protect against these kinds of things, says her partner, Martynas.

And we can't even fight, like, simple balloons. We're not even prepared for the basic stuff.

Additional reporting by Eve Webster