The US and the UK are exploring ways to step up their campaign against Houthi militants in Yemen without provoking a broader war, with a focus on targeting Iranian resupplies and launching more aggressive pre-emptive strikes, people familiar with the matter said. The proposals could mark an escalation in the allied effort to end the chaos in the Red Sea, which handled about 12 per cent of global trade before the Houthis began targeting commercial ships in response to Israel's bombardment of the Gaza Strip.<br />''<br />''The Houthi attacks has led to higher insurance costs and provoked fears of fresh inflationary pressure as ships take a longer and costlier route around the southern tip of Africa. Meanwhile, the Houthis have vowed to step up their attacks in the week since the allies began targeting them. A series of US and UK strikes against the Houthis so far has not deterred the group or degraded its ability to target commercial shipping. <br />