THE FTSE 100 put in a lacklustre performance at the end of the week as Donald Trump turned up the heat on the US trade war with China.

The US president has threatened to impose tariffs on $500 billion (£377bn) worth of Chinese goods, having already slapped tariffs on $34bn worth of imports.

China has responded with a 25 per cent tariff on hundreds of agricultural, cars and seafood products, worth $34bn in total.

China's prime minister Li Keqiang has said his country will defend itself against other nations' tariffs.

China has filed a complaint with the World Trade Organisation over the US actions.

Gregory Daco, head of US economics at Oxford Economics, said: "We believe these tariffs will reduce real GDP by 0.1% in each economy.

"The automotive, aircraft and agricultural sectors would see disproportionately larger hits to activity.

"This would be felt both in the US, but also abroad since some large US multinationals have significant operations in China."

He said the tariffs would impact consumer goods, disrupt global supply chains, and weigh on stock markets.

By the market close, the FTSE 100 was up 0.19% or 14.48 points to 7,617.7.

The Cac 40 in France was up 0.18%, while the Dax in Germany rose 0.26%.

In currency markets, the pound was up 0.33% against the dollar at 1.326.

Against the euro, sterling was flat at 1.129.

Brent crude prices were down by 0.84% to $76.902 per barrel during trading.

Productivity relapsed in the first quarter of the year, with economists warning that there is still work to do if the UK hopes to solve its "productivity puzzle".

Figures from the Office for National Statistics (ONS) showed productivity fell 0.4% in the three months to the end of March, as compared with the prior quarter, the first contraction for a year.

The ONS said the fall was due to strength in employment growth combined with weaker growth in output.

In UK stocks, Rolls-Royce agreed to sell its loss-making commercial marine business to Norwegian firm Kongsberg for an enterprise value of £500 million.

The Derby manufacturer said the net proceeds will be around £350m to £400m after taking pension liabilities and other costs into account.

The announcement comes as Rolls-Royce enacts a sweeping restructuring plan aimed at saving £400m per year. Shares were flat at 985.6p during trading.

British satellite firm Inmarsat's shares slumped after it rejected a second takeover approach from US rival Echostar worth £3.2bn.

Echostar confirmed on Friday that it put forward a "new and improved proposal" earlier this week which offered shareholders 265p per share in cash and an exchange of 0.0777 Echostar stock for each Inmarsat share.

That offer is equivalent to 532p per Inmarsat share and would value the company at £2.45bn. By the close, Inmarsat's shares were down 8.02% or 42.2p to 483.8p.

The biggest risers on the FTSE 100 were ITV up 7.4p to 180.4p, Severn Trent up 43p to 2,068p, National Grid up 17.4p to 876.5p and Vodafone up 3.36p to 191p.

The biggest fallers on the FTSE 100 were Associated British Foods down 112p to 2,492p, Direct Line Insurance down 12.7p to 330.2p, Rightmove down 140p to 5,076p, Fresnillo down 26p to 1,123.5p.