Afghanistan's communications infrastructure has become the latest casualty of the intensified war between Nato and the Taliban, with mobile phone companies reporting crippling attacks on their network of transmission masts.

The onslaught came in the wake of a decree by Hamid Karzai ordering phone companies to defy insurgent demands to shut down transmission networks in large parts of the country during the night.

The mobile phone networks are a key battleground in the war on the Taliban as the vast majority of anti-insurgent tipoffs from Afghan civilians are made at night, through phone calls.

The phone industry says the damage has been so great that the numbers of hours of coverage available to all phone users has fallen significantly – the first time there has been such a fall.

After a decade of explosive growth in public access to phones, which are now part of everyday life for millions of Afghans, the falloff is an extraordinary change of fortunes for an industry that is often cited as one of the country's biggest post-2001 success stories.

The Taliban began attacking transmission masts in 2007, but the damage was limited and the attacks were often aimed only at extorting money from companies.

But since mid-summer attacks have soared, with up to 30 towers being destroyed or damaged in one 20-day period. Previously a loss of five would be considered a bad month.

Insurgents have also become much more destructive.

"They used to just blow up our fuel tanks," a senior executive of an Afghan telecoms company said. "Now they put fuel inside the control room with all the equipment, absolutely destroying everything."

Some masts have even been blown completely out of the ground by insurgents wiring them up with huge quantities of explosives.

And they have focused many attacks on critical hub relay towers, which has the effect of bringing down services in many other locations. In some cases entire provinces have lost all phone services for days on end.

"We have heard that the Taliban now have telecom engineers advising them on how they should attack our sites," said another executive from one of the country's main phone providers.

By forcing a night-time communications blackout the Taliban demonstrate the continued weakness of the Afghan government, western officials say.

But it is stopping anti-insurgent tipoffs that is really key.

"If the masts are off Afghans can't report anything," said Beth Bierden, the US military director of Telecommunication Advisory Team, based at Nato's headquarters in Kabul. "If you see an insurgent you can't call the police to say check this out."

Special forces' night-time kill and capture operations also substantially rely on intelligence gleaned from tipoffs and phone intercepts.

Not surprisingly the US has made several efforts to drag the telecom companies into the war effort, even to the extent of spending tens of millions of dollars on a largely unused parallel phone system.

But after 12 July the Afghan government also joined the campaign to force the country's mobile phone companies to defy the Taliban after Karzai, sitting in his presidential palace in Kabul, was unable to call friends, allies and government officials in the key southern city of Kandahar.

Earlier that same day the president's powerbroking brother, Ahmed Wali Karzai, had been shot dead by his own bodyguard and the president was frantically working out how to retain his family's grip on Kandahar.

Furious, Karzai then issued a decree ordering the phone companies to turn on their masts or risk losing their licenses.

Kandahar City has enjoyed 24-hour coverage ever since, but the Taliban responded by ratcheting up their attacks.

Despite US and government pressure the phone companies have still not completely complied, fearing even more attacks on their masts, offices and staff if they agree.

"We're not going to turn on our masts and become part of the army of the Afghan government," said an executive. "I'm not going to switch on my sites because my towers are being attacked, my people are being attacked and the government is not doing anything to help me."

The US has spent millions of dollars finding other ways to bring round-the-clock phone calls to the insurgency's heartlands.

One $68m initiative involved building 20 masts on secured Nato bases deep inside Taliban territory in the Helmand river valley and along the southern portion of Highway One. They hoped villagers would then roam on to the US-provided network after the main carriers turned off their masts in the evening.

But all four major phone companies refused to co-operate, fearing the rest of their network would be attacked, not just in insecure areas, but also in more stable parts of the country.

Even clever technical fixes to conceal the identity of the phone company carrying the calls were rejected.

"They said it was going to be anonymous, but some Talib sitting in Sangin can't read English anyway," the tower provider said. "He is not going to know which company it is, but he'll attack them all the same."

The industry's rejection of the plan means that although all 20 masts are on, almost no one is using them. Calls can only be made with a US-military-provided sim card, and callers can only make emergency calls to the police and army within the same tiny network.

In the words of one telecoms expert, the US-built network is almost certainly "the most expensive phone network in the world" on a per user basis.

The industry is also appalled by the huge price tag put on a barely used network, with one executive calculating that for $68m most companies could have built almost 300 masts.

Bierden conceded that the project was not gaining as many callers as they wanted, but insisted the programme would be expanded.

Future plans include an additional 23 district capitals receiving the US-provided phone masts.

The hope is the US towers will eventually be handed over to Afghan Telecom, a state-owned company that does not have its own GSM network.

"By putting these networks out there, we can help solve that security problem," Bierden said. "By allowing people to talk to each other the insurgents don't have the upper hand."