SHANGHAI (Reuters) -China intervened on Monday to support domestic stocks plunging on U.S. tariff woes, with a sovereign wealth fund increasing its holdings in equities and saying it would defend market stability. Central Huijin Investment, a unit of China Investment Corp, said in statement it has added China-listed shares via exchange-traded funds and will continue to increase holdings to "safeguard the smooth operation of the capital market." The Shanghai Composite Index lost 7% on Monday in its worst day in five years, reeling after the U.S. imposed extra tariffs of 34% on China last week which then fired back with its own 34% levies.