Shares in the operator of Europe's largest fibre-optic data network, KPNQwest, fell by 71% after they resumed trade following the company's bankruptcy on Friday.

By 1150 GMT KPNQwest shares were down 67.7% at 10 euro cents, valuing it at 5m euros ($4.7; �3.2m) compared with 42bn euros two years ago.

"What has happened is unbelievable," said Philip Scholte, telecoms analyst at Stroeve brokerage in Amsterdam.

"It's difficult for me to accept that business has deteriorated this badly in only a couple of months," he added.

Slower connections

Austria's biggest broadband internet provider said KPNQwest's bankruptcy was causing the internet to slow down.

UPC Telekabel said connections within Europe were unchanged but there were problems connecting with other continents.

The company warned that the slowdown could spread to affect the general internet service across Europe.

The Euronext stock exchange has said it will delist KPNQwest from the main indices on Thursday.

Possible buyers

Its share collapse comes despite KPNQwest's assurance that there are buyers for its main assets.

"There are several potential buyers, but AT&T is the most likely one," a KPNQwest spokesman said.

He added that the US telecoms company was conducting due diligence at the firm's headquarters in the Netherlands.

AT&T has declined to comment on the issue.

Struggling with debts

In February, KPNQwest said it had enough money and in mid-May it said credit protection was not an option.

One week later it asked for protection from creditors, and then on Friday filed for bankruptcy.

The company's parents - Dutch carrier KPN and US telcoms operator Qwest - are also struggling with their debts.

Analysts have said KPNQwest's network could fetch between 200m and 250m euros.

But sales talks will be complicated by the fact that some of its units will be liquidated separately, while others have decided not to seek protection.