Houthis say Red Sea route remains free to use, pushing back on report of new shipping fees.
The Houthis' blockade of Bab al-Mandeb threatens a vital global trade route.
About 6 million barrels of crude per day that pass through the strait to Asia are now at risk, experts say.
If the fighting in Yemen expands, and the Houthis try to block the Bab al-Mandeb, the world economy faces a new shock.