The news, for which Kyodo did not cite sources, comes at a time of heightened scrutiny of Chinese tech firms by Washington and some prominent allies over ties to the Chinese government, driven by concerns they could be used by Beijing for spying.

Japan's big three telecom operators plan not to use current equipment and upcoming fifth-generation (5G) gear from China's Huawei Technologies Co Ltd and ZTE Corp, Kyodo News reported on Monday.

The ZTE logo is seen on an office building in Shanghai on May 3, 2018.

Last week sources told Reuters that Japan planned to ban government purchases of equipment from Huawei and ZTE to ensure strength in its defences against intelligence leaks and cyber attacks.

A SoftBank Group Corp spokesman said Japan's third-largest telco was closely watching government policy and is continuing to consider its options. The amount of equipment in use from Chinese makers "is relatively small", he said.

The country's top two telecommunications operators, NTT Docomo Inc and KDDI Corp, said the firms had not made any decision yet.

Docomo does not use Huawei or ZTE network equipment, but it has partnered with Huawei on 5G trials. KDDI also does not use Huawei equipment in its "core" network, a spokeswoman said, adding it does not use any ZTE network equipment.

Huawei did not respond to Reuters request for comment, while ZTE declined to comment.

Huawei has already been locked out of the U.S. market, and Australia and New Zealand have blocked it from building 5G networks amid concerns of its possible links with China's government. Huawei has said Beijing has no influence over it.

Japan's decision to keep it out would be another setback for Huawei, whose chief financial officer was recently arrested by Canadian officials for extradition to the United States.

World financial markets have been roiled since news of the arrest, on worries it could reignite a Sino-U.S. trade row that was only just showing signs of easing.

Shares of SoftBank, which has the deepest relationship with Huawei among the big Japanese telcos, fell the most among the three top Japanese telcos on Monday, ending down 3.5 percent.