Brent crude traded near a six-week high amid concern that the escalating crisis in Ukraine will disrupt supplies. West Texas Intermediate rose for a second day.

Futures advanced as much as 0.2 percent in London before retreating. Ukraine accused Russia of fueling terrorism in its eastern regions as the North Atlantic Treaty Organization pledged to bolster the defenses of nearby nations. WTI rose after Janet Yellen, in her first speech to a Wall Street audience since becoming Federal Reserve chair, emphasized her commitment to support the U.S. economic recovery.

“The escalating crisis in Ukraine provides strong support to the market amid concerns about oil supply issues in the region,” Myrto Sokou, an analyst at Sucden Financial Ltd. in London, said in an e-mail. “Yellen comments yesterday spread an optimistic tone in the WTI contract amid hopes for a strong U.S. economic recovery.”

Brent for June settlement was 37 cents lower at $109.23 a barrel as of 12:47 p.m. on the London-based ICE Futures Europe exchange. The European benchmark crude was at a premium of $6.30 to WTI for the same month. The spread widened for a third day yesterday to close at $6.57.

WTI for May delivery rose as much as 52 cents to $104.28 a barrel in electronic trading on the New York Mercantile Exchange and was down 2 cents $103.74 a barrel. The contract added 1 cent yesterday. The volume of all futures traded was about 25 percent above the 100-day average. Prices have gained 5.4 percent this year.