* Alibaba to invest 100 bln yuan over 5 years on logistics
* To lift stake in Cainiao to 51 pct with 5.3 bln yuan investment
* Cainiao the focus of US SEC 2016 probe into Alibaba's accounting (Recasts, adds details)
HONG KONG/BEIJING, Sept 26 (Reuters) - Chinese e-commerce firm Alibaba Group has taken control of logistics unit Cainiao and pledged to spend 100 billion yuan ($15 billion) over five years to build out a global logistics network, underscoring aggressive expansion plans overseas.
Alibaba will invest 5.3 billion yuan to boost its stake in Cainiao Smart Logistics Network to 51 percent from 47 percent, giving it direct control over the loss-making affiliate, suggesting a rough valuation of Cainiao at around $20 billion.
The announcement comes as Alibaba rapidly expands its e-commerce and logistics network abroad to diversify its consumer base, including newly announced direct sales channels in counties around Southeast Asia.
"Our commitment to Cainiao and additional investment in logistics demonstrate Alibaba's commitment to building the most-efficient logistic network in China and around the world," Alibaba CEO Daniel Zhang said in a statement on Tuesday.
Cainiao was the focus of an investigation last year by the U.S. Securities and Exchange Commission (SEC) into Alibaba's accounting practices.
Alibaba, which will gain an extra seat on Cainiao's board giving it four out of a total seven seats, added that more shares were issued in the funding round to other investors. It did not give details about the other issuances, which would impact Cainiao's valuation.
The investment also signals Alibaba's intention to boost control over China's domestic warehousing and delivery market, increasingly competitive as firms seek to make use of troves of logistics data about the country's Internet-savvy shoppers.
The firm, headed by billionaire magnate Jack Ma, said that the longer-term $15 billion investment would be used to develop its data technology and improve its warehousing and delivery.
The battle to control logistics networks in China has at times created tensions between e-commerce and delivery firms.
In June major logistics company SF Holding cut ties with Cainiao, which provides logistics support directly to Alibaba's top e-commerce platform Taobao. SF Holding claimed Alibaba had requested data unrelated to an existing partnership agreement. Alibaba denied the claims.
Chinese logistics firms have also attracted billions of dollars from equity investors, though many have faced challenges with recent public listings.
Shares of ZTO Express Inc, which raised $1.4 billion from a New York IPO last October, are down 22 percent from the listing price to-date. Best Inc, a Chinese delivery firm backed by Alibaba, raised under half of what it had initially intended to in a U.S. IPO last week.
A person close to Alibaba, who asked not to be named, said Cainiao was not currently considering an IPO.
Alibaba and Cainiao declined to comment.
Alibaba co-founded Cainiao in 2013, with partners including department store owner Intime Group, conglomerate Fosun Group and a handful of logistics companies. It oversees roughly 57 million deliveries a day. ($1 = 6.6130 Chinese yuan renminbi) (Reporting by Kane Wu in HONG KONG and Cate Cadell in BEIJING; Writing by Adam Jourdan; Editing by Muralikumar Anantharaman)