UPDATE 1-European shares retreat on escalating U.S.-China trade row

* China unveils new tariffs on U.S. products

* U.S. futures tumble

* WPP declines(Adds China unveiling new tariffs, stocks)

By Julien Ponthus

LONDON, April 4 (Reuters) - Losses on European exchangessteepened on Wednesday after China unveiled new tariffs againstU.S. products, increasing concerns of an escalating tradestandoff between the two countries.

The pan-regional STOXX 600 index and Germany'sexporter-heavy DAX hit a session low, down 1 percentand 1.4 percent respectively after China said it would imposeadditional tariffs of 25 percent on 106 U.S. goods.

U.S. stocks futures also fell sharply. Nasdaq futureswere down 2.1 percent, S&P 500 futures fell 1.6percent and Dow Jones futures tumbled down 1.8 percent.

The tension could also be felt on the Chinese yuan, whichsuffered its biggest daily fall versus the dollar in two weeksand through lower yields for top-rated U.S. and Europeangovernment bonds.

"China has taken out big guns to answer Trump’s tariff, thetrade war is here", Naeem Aslam, chief market analyst at ThinkMarkets, said.

The European tech sector posted the worstperformance with a fall of 1.6 percent, while cyclical stockssuch as financials and industrials also weighed heavily.

WPP was among the biggest fallers at the open afterthe British advertising group said it was conducting aninvestigation into an allegation of personal misconduct againstits chief executive, Martin Sorrell, who denied any wrongdoing.

The shares gradually recouped some of their losses and weredown 1.5 percent at 0856 GMT.

Swiss Re was down 3.1 percent after the reinsurersaid Japan's SoftBank was in talks to buy a stake whichis unlikely to exceed 10 percent.

Bloomberg reported on March 29 that SoftBank was looking tobuy a 25 percent stake in Swiss Re, worth about $9.6 billion, aspart of its drive to broaden its investments, which include its$93 billion Vision Fund for technology projects.

German IT-leasing specialist Grenke was the bestperforming stock, up about 5.9 percent after a positive tradingupdate for the first quarter.(Reporting by Julien Ponthus, Editing by Kit Rees and AlexanderSmith)