Norwegian Authorities Investigate Embassy Attack
Frode Larsen, Oslo police head, called the attack 'natural' in current security context.
Eyewitnesses reported three 'bangs,' smoke, and consular entrance damage.
No injuries reported, but police search for perpetrators.
U.S. State Department and Norway's government investigate the attack.
Possible link to U.S.-Israeli war on Iran.
Norway's police kept threat level unchanged.
U.S. State Department issued travel caution advisory.
2 hours ago