This is the first deadly clash on this border in 45 years.

Initially, the Indian army said three soldiers had died and others were wounded.

But now we have this updated statement saying 17 troops were critically injured at the standoff location and who were exposed to sub zero.

Temperatures in the high altitude terrain have succumbed to their injuries, and so the death toll is now 20.

China, for its part, is accusing India of crossing the border and attacking its personnel.

Well, let's have a look at the border in question.

This is the gallon River Valley area.

Both sides have been deploying thousands of troops on either side in recent weeks.

Well, I speak to Shashank Joshi, defense editor of The Economist, who is live with us.

Thank you very much for your time before we get into the details of the last 24 hours or so.

Help us understand why tensions have been growing in the last few weeks.

Sure, well, this is a strategic area for India.

It's right up in the far north for China.

This is on the western edge of Tibet, Askew pointed out.

This is the first major attacks since 1975 and that's partly because they both learned how to manage their differences.

The border is absolutely enormous.

ITT's almost entirely undefined, so patrols effectively overlap.

The reason tensions have been growing in the last few weeks isn't entirely clear.

But it's probably to do with the fact that India has been upgrading the infrastructure on its own side of the border in this area known ASL ADAC.

Over the past several years, particularly over the past year, they've completed a vital road that runs south to north.

And what seems to have happened is the Chinese side has interpreted that as a challenge to the status quo on a threat to their own forces on the Chinese side, effectively to the east, on with regard to the particular circumstances in which these 20 Indian soldiers die, do you have any detail, a tool?

We have some details from Indian accounts, although how reliable they are is open to question.

What appears to have happened is a few days ago, the Indian and the Chinese size, agreed to effectively diffuse the crisis.

They agree to disengage from several positions.

The standoff is in three places.

The gallon river valley is one of them, the other to a pan gone lake to the south.

On the other one is called Hot Springs, which is also to the south.

The Chinese site appears to have agreed to disengage from at least two of those, including gallon Valley.

What seems to have occurred as an Indian patrol was waiting to meet the Chinese side to discuss details of that withdrawal of the details of that disengagement so that both sides would move several kilometers back.

We don't know exactly what transpired, but that seems to have devolved into a fight.

Now.

Troops on both sides don't use weapons because they have various protocols, and agreements do not do so over the years.

But the Chinese side appears to have used stones.

Clubs sticks with nails in them, according to some Indian accounts, to attack the Indian side, many of whom subsequently were critically injured.

And some of you may have fallen in some way in that punishing terrain and succumbed to frostbite or exposure overnight many others may have succumbed to their injuries from that from that conflict itself that have also been some Chinese casualties.

But we don't know how many, and we don't know if there've been any fatalities.

And as we listen to these extraordinary accounts coming in, what's the strategic context here?

Aside from the national pride of these moments being played out on the international stage wire, both countries so focused on this particular border well, let's remember here that India in China, and not just Asia's two biggest rising powers or two of the world's most important rising powers they fought a war over this patch of land back in 1962 a war in which China essentially rapidly defeated India and that has been a historical trauma for India in subsequent decades.

Now they stabilize the border in many ways.

As you said, there hasn't been a shot fired since 1975.

This is the worst clash since 1967 but at the same time they have been competing for influence all over Asia.

India doesn't like the fact that China is allied very closely to Pakistan that in the Chinese navy's is increasingly busy in the Indian Ocean.

And, of course, China doesn't like the fact that India, in India's if successive Indian governments have moved ever closer to the United States, China's rival.

And so the geopolitical context effectively compounds the local tensions at the border itself, making for a very volatile mix.