* China seeks WTO backing to impose sanctions on U.S.
* Apple gains ahead of expected new iPhone launches
* Western Digital drops on NAND price worries
* Indexes up: Dow 0.5 pct, S&P 0.5 pct, Nasdaq 0.6 pct (Updates to late afternoon)
By Caroline Valetkevitch
NEW YORK, Sept 11 (Reuters) - U.S. stocks rose in afternoon trading on Tuesday after a subdued start, as Apple led a jump in technology shares.
Apple rose 2.6 percent, boosting the three major indexes, a day ahead of an highly anticipated event in which the company is expected to unveil new iPhone models.
The technology sector gained 0.9 percent, on pace for its biggest jump in two weeks, also boosted by Microsoft , up 1.6 percent, and Facebook, up 1.2 percent.
"That's been the main fuel for the market," said Alan Lancz, president of Alan B. Lancz & Associates Inc, an investment advisory firm, based in Toledo, Ohio. "Maybe tech has taken the punch and is recovering, and investors are getting more confident that the leader is back."
The energy index, up 1.2 percent, helped to lift the S&P 500. Oil prices rose after U.S. sanctions squeezed Iranian crude exports and tightened global supply.
At 2:59 p.m. ET, the Dow Jones Industrial Average rose 133.94 points, or 0.52 percent, to 25,991.01, the S&P 500 gained 13.03 points, or 0.45 percent, to 2,890.16 and the Nasdaq Composite added 47.00 points, or 0.59 percent, to 7,971.16.
Also gaining were shares of companies that could see a boost in sales in the aftermath of Hurricane Florence, which was upgraded to Category 4 ahead of landfall on Friday.
Home improvement retailers Home Depot and Lowe's also rose, while shares of construction material companies gained slightly.
Trade tensions continued to linger after China told the World Trade Organization it wanted to impose sanctions on the United States for its non-compliance with a ruling in a dispute over U.S. dumping duties.
President Donald Trump had on Friday threatened to slap tariffs on nearly all Chinese imports.
Western Digital slid 3.7 percent after RBC echoed other brokerages in warning that falling NAND chip prices would hit the company.
Advancing issues outnumbered declining ones on the NYSE by a 1.23-to-1 ratio; on Nasdaq, a 1.16-to-1 ratio favored decliners.
The S&P 500 posted 37 new 52-week highs and 14 new lows; the Nasdaq Composite recorded 95 new highs and 91 new lows. (Additional reporting by Shreyashi Sanyal in Bengaluru; Editing by Arun Koyyur Editing by Nick Zieminski)