刚刚——伦敦美国大使馆发布安全警报，敦促在英国的美国人在公共场所保持高度警惕，称“恐怖袭击极有可能发生”。该警报发布之际，英国当局将全国恐怖主义威胁级别提升至“严重”。

JUST IN - U.S. embassy in London issues security alert urging Americans in the UK to exercise increased caution in public spaces stating "a terrorist attack is highly likely." The alert comes as British authorities elevate the national terrorism threat level to "severe."