By Sam Nussey

TOKYO (Reuters) - SoftBank Group Corp's mobile phone services were disrupted in some parts of Japan on Thursday, ahead of an initial public offering (IPO) of its domestic telecoms unit later this month that will potentially raise $21 billion.

Some customers at Japan's third-largest telco have been unable to make calls or use the internet in the hours following the onset of connection problems at 0439 GMT.

The network issues, which stemmed from problems at exchanges for high-speed wireless LTE network, are on the way to resolution, a SoftBank spokeswoman told Reuters.

SoftBank has 40 million mobile users.

Shares of the group fell as much as 6 percent after news of the disruption, pressured by a broader market sell-off following the arrest of the global CFO of Huawei Technologies. The two companies have partnered on 5G trials.

Shares of SoftBank Group's telco unit, SoftBank Corp, are set to debut on the Tokyo Stock Exchange on Dec. 19. The group will set a final offering price on Dec. 10.

Strong retail demand saw SoftBank last week forgo a price range for the bumper IPO, setting a single indicative rate of 1,500 yen ($13.30).

Shares of the group closed down 5 percent, as the broader market skidded to a two-week low after Canada arrested Huawei's Meng Wanzhou at the request of the United States, threatening a new spike in Sino-U.S. tensions.

($1 = 112.8200 yen)

(Reporting by Sam Nussey, Chang-Ran Kim and Elaine Lies; Editing by Himani Sarkar)