BondCliQ aggregates pre-trade bid and offer quotes for company bonds and has just over 40 participating dealers, averaging 70,000 quotes on 15,000 bonds daily.

The money from LSEG, with Aflac Ventures and SEI also participating in the completed initial Series A whip round, will help to create a more transparent corporate bond market, BondCliQ said in a statement on Tuesday. Investment manager Vanguard has become a strategic partner.

Bond trading in the United States is dominated by Wall Street's giant banks, with market transparency lagging that of the stock market, making it hard for investors to determine what the real price is, especially in volatile markets.

The money will partly be used to expand into additional corporate bond markets, such as Europe.

"We already have some prominent dealers in Europe, they are providing their dollar denominated markets, so we are not that far away from being able to launch a product in Europe that organises euro denominated and sterling denominated corporate debt," BondCliQ CEO Chris White told Reuters.

The latest backers give credibility to having more transparency in bond markets, White said.

"When it comes to the larger dealers, we are optimistic that they will want to join this initiative and actually help to make the market healthier," White added.

LSEG's investment is a further instance of the exchange group diversifying beyond its equities roots and into fixed income and data following its $27 billion acquisition of data and analytics group Refinitiv a year ago.

Thomson Reuters, parent of Reuters News, holds a minority stake in LSEG and Refinitiv pays Thomson Reuters for news it distributes.

(Reporting by Huw Jones; editing by Emelia Sithole-Matarise)

By Huw Jones