Rising trade tensions sends FTSE 100 lower

* FTSE 100 down 0.4 pct at close

* Indivior (Frankfurt: 2IVA.F - news) tumbles 6 pct after patent litigation loss

* GSK up after exits Pfizer (NYSE: PFE - news) consumer health bid

* Asia-exposed funds tumble (Updates prices at close)

By Helen Reid

LONDON, March 23 (Reuters) - Mounting fears of a global trade war after the U.S. slapped tariffs on imports from China sent British stocks to a 15-month low on Friday.

The FTSE 100 ended the session 0.4 percent lower at 6,921.94 points, clawing back some losses after hitting its lowest level since December 2016 in early trading.

Investor (LSE: 0NC5.L - news) unease extended to the response from China, which urged the United States to "pull back from the brink", and unveiled its own plans to impose tariffs on up to $3 billion of U.S. imports.

Bank stocks and miners were the biggest drags as risk sentiment soured and the most trade-sensitive sectors suffered.

Some felt this was a long-overdue selloff in stock markets, which enjoyed an unusually robust 2017 but have run into obstacles since the start of last month.

"It could have been anything that caused it, it just happened to be trade," said Daniel Lockyer, senior fund manager at Hawksmoor Investment Management.

"The market is a discounting mechanism and we didn't think it was discounting enough risks out there, whether it's corporate earnings disappointing, political risks, the end of QE," he added.

Indivior shares plummeted more than 20 percent at the open before recovering, ending down 6.3 percent, after the pharma firm lost a patent protection case, setting it up for cheap competition to its opioid addiction treatment.

A U.S. court ruled generic drugs firm Alvogen had not infringed three of the British firm's patents, a blow to Indivior whose Suboxone Film treatment accounts for as much as 80 percent of its revenue.

GSK rose 3.3 percent after it pulled out of the bidding war for Pfizer's consumer health business after Reckitt Benckiser (Xetra: A0M1W6 - news) did likewise earlier this week.

Smiths Group (Frankfurt: QS2A.F - news) dropped 4.4 percent to the bottom of the FTSE 100 after reporting a weaker first-half profit than expected. The engineering group pointed to currency headwinds and higher R&D costs.

Next (Frankfurt: 779551 - news) bounced 7.7 percent to the top of the index after its annual results, with investors relieved the clothing retailer did not issue a profit warning.

A broadly challenging retail environment has caused many of Britain's high street stores to suffer sharp losses, making Next (EUREX: NXTJ.EX - news) a relative winner.

UK-listed funds invested in Japan and China were among the worst performers on the mid- and small-cap indexes after a rout in Asian trading overnight.

Baillie Gifford Japan Trust fell 2 percent, while Fidelity China Special Situations tumbled 3.1 percent. Among small-caps Fidelity Japanese Value shares dropped 3.4 percent and Schroder Japan Growth Fund lost 1.4 percent.

(Reporting by Helen Reid and Kit Rees Editing by Andrew Heavens and John Stonestreet)