Shares of the group fell as much as 6 percent after the news, pressured also by a broader sell off in stocks following the arrest of a senior executive at Huawei Technologies . The two companies have partnered on 5G trials.

A SoftBank spokeswoman said connection problems started around 1:39 p.m. (0439 GMT). Other details, including when full service will be restored, are not yet known, she added.

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

SoftBank will set a final offering price on Dec. 10 with shares set to begin trading on Dec. 19.

Shares of the group closed down 5 percent on Thursday, in a broader market that skidded to a two-week low after Canada arrested Huawei's global chief financial officer Meng Wanzhou at the request of the United States, threatening a new spike in Sino-U.S. tensions.  ($1 = 112.8200 yen)