TOKYO, Feb 15 (Reuters) - Japan's Nikkei share average gave up early gains to end the morning session lower on Tuesday, after disappointing financial results handed big losses to index heavyweights Recruit Holdings and Kubota.

Sentiment also continued to be weighed down by worries about accelerated U.S. monetary tightening and the threat of conflict in Ukraine.

The Nikkei slumped 0.27% to 27,006.66 as of the midday break, after opening up 0.38%.

Staffing services company Recruit tumbled 12.32% making it both the Nikkei's biggest percentage decliner and biggest drag by index points.

Construction machine maker Kubota tanked 11.34%.

The United States warned on Monday that Russia could soon invade Ukraine, pushing up energy prices and ramping up the risk of market volatility at the same time investors are fretting about the potential for the Federal Reserve to hike interest rates by half a percentage point next month.

"Amid the earnings reports we're getting a new set of negative drivers like rising oil prices and Ukraine tensions, making it hard to chase stock prices higher," said a market participant at a domestic securities firm.

Other notable decliners included chipmaking giant Tokyo Electron, which sank 0.74%, and startup investor SoftBank Group, which lost 1.18%.

Toyota Motor retreated 0.71% and Sony Group gave up 2.20%.

Financials were the Nikkei's worst performing sector, dropping 1.64%, as a pullback in global long-term bond yields cut the outlook for profits.

The broader Topix slipped 0.23%. A 0.32% decline in the value share index outpaced a 0.13% slide for growth shares.

At the other end, logistics company Nippon Express Holdings jumped 9.50% following a positive earnings report, making it the Nikkei's biggest percentage riser.

Advertising giant Dentsu rallied 6.74%, also on favorable financial results, to be the biggest gainer by index points. (Reporting by Tokyo markets team; Editing by Shailesh Kuber)