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* FTSE 100 down 0.8%
* FTSE 250 down 0.7%
* Oil, banks biggest drags to main index
* Kier at 18-1/2-yr low after profit warning
June 3 (Reuters) - London’s main stock market index fell almost 1 percent to a near 12-week low on Monday as an exchange of trade threats between Washington and Beijing stoked fears of a slide into recession within a year as economic data from Asia again disappointed.
Builder Kier was the biggest faller on the midcap FTSE 250 index, down 22% after warning on profits for 2019.
The main FTSE 100 index was trading down 0.8% at its lowest level since March 12 by 0710 GMT, while the midcap index lost 0.7%.
China added to existing tensions over the weekend by warning the United States not to meddle in security disputes over Taiwan and the South China Sea, while Donald Trump also vowed to impose punitive tariffs on all Mexican goods.
Sectors which are more vulnerable to a disruption in international trade were hit across the board, with 1% falls for oil majors Shell and BP leading the losses among blue-chip shares. (Reporting by Muvija M and Shashwat Awasthi in Bengaluru; editing by Patrick Graham)