(Yicai Global) July 25 -- E-commerce giant JD.Com Inc. [NASDAQ:JD] recently stopped its merchants using TTK Express, a courier affiliated with online retail rival Suning Commerce Group Co. [SHE:002024], due to substandard services.

The move triggered a war of words between executives of the two e-commerce platforms, and suggests that the fierce competition seen in China's online retail sector is intensifying.

Sun Weimin, vice president of Suning Commerce Group, complained that JD.Com's review of TTK was unfair in a microblog posted around mid-day yesterday. The review said TTK Express offers "the worst service on its entire network platform".

JD.Com has abused its power, exceeded its authority, and interfered with the discretion of a third party, Sun said.

Suning, originally one of China's major home appliance sellers, has become an important retailer both on and offline since the company implemented a digital sales strategy. The firm, and China's other internet giant Alibaba Group Holding Ltd. [NYSE:BABA], maintain close cooperative ties and also hold stakes in each other.

A JD Logistics spokesperson responded saying that Sun had a "fragile heart" and that following Suning's acquisition of TTK's service outlets, the company had not delivered any orders from Suning.com. This shows that not even Suning trusts the service quality at TTK Express, he said.

The decision to suspend cooperation with TTK Express was made due to a large number of consumer complaints against the courier's timeliness and quality of service, as well as other irregularities, the spokesperson insisted.

JD.com notified merchants on its platform that it would close the TTK Express service interface on July 19, after it ranked last in terms of service quality and user satisfaction following reviews for the first half of this year.

In a statement issued a statement on the evening of July 20, the courier condemned the firm and dubbed its reasons for the move absurd.