Yemen must not become another Afghanistan but Britain's role is to "stay close" and offer it assistance rather than send in troops at this stage, the new head of the UK's Armed Forces said.
Chief of the Defence Staff General Sir David Richards said the military's concentration needed to remain on Afghanistan - to prevent that country becoming a "second Yemen".
Global attention has once again been focused on Yemen, the country which spawned al Qaida, after it emerged as the source of ink cartridge bombs found on aircraft last week.
Asked if an Afghan-style military intervention was the right approach, Gen Richards told the BBC Radio 4 Today programme on Monday: "It might be but right now it is not considered to be the case and clearly the Yemeni government does not believe it needs our help and they are extremely on-side, like most Islamic nations are actually."
He said: "Clearly, the primary agency dealing with this are our intelligence and security agencies. But the military are already helping with their training.
"I don't think we want to open up another front there and nor do the Yemenis want us to do that. So we have to find other ways of doing these things and in the meantime making sure Afghanistan doesn't revert to becoming, if you like, a 'second Yemen' - that is the Army's primary duty at the moment.
"Our role is to remain very close to them, to help them where they most need it and in the meanwhile focus our efforts on Afghanistan and assisting Pakistan to ensure they don't become the threat Yemen is beginning to be.
"When people say Yemen is worse than Afghanistan or Pakistan, one reason is that many of al Qaida's leaders and operatives spend most of their time thinking about their own security rather than planning how to attack us."
Gen Richards, who succeeded Air Chief Marshal Sir Jock Stirrup on Friday, said there were "reasons to be cautiously optimistic" about progress in Afghanistan where the allied effort was "just beginning to" turn the tide.
He said he was "pretty relaxed" about Prime Minister David Cameron's 2015 target for withdrawing combat troops, saying the timescale "sharpens our attention" and helps ensure resources are put in.