A year ago the CIA sent many of its top field operatives with counter-terrorism experience to the country, while some of the most secretive US special operations commandos began training Yemeni security forces in counter-terrorism tactics.
The Pentagon will be spending more than $US70 million ($79m) over the next 18 months and using teams of special forces to train and equip Yemeni military, Interior Ministry and coast guard forces, more than doubling previous military aid levels, The New York Times reported.
Yemen became the focus of US attention at the weekend after a Nigerian man, who tried to blow up a Detroit-bound plane on Christmas Day, confessed to training with an al-Qa'ida bombmaker in Yemen.
One US official briefed on the inquiry said investigators were still trying to determine whether the suspect's claims of links to al-Qa'ida in Yemen were accurate, and how strong those ties were.
The FBI's office in Yemen is working with authorities there to track any recent travel by Abdulmutallab in that country.
US officials say the accused man's father, a prominent banker in Nigeria, had warned officials at the US embassy in Lagos in recent weeks he feared his son had been "radicalised" during trips outside the West African country.
The father's concerns about his son were not specific, nor did they point to any imminent threat against the US, according to a US official. But they were enough for US authorities to add his name to a broad terrorism database called Terrorist Identities Datamart Environment. People on the list are not precluded from boarding flights to the US.
Abdulmutallab was not added to more sensitive databases, such as the so-called "no fly" watch list, that would have flagged him for additional screening or barred him from boarding a US-bound flight.
Yemen has long been a refuge for jihadists, in part because Yemen's government welcomed returning Islamist fighters who had fought in Afghanistan during the 1980s. But al-Qa'ida militants have made much more focused efforts to build a base in Yemen in recent years, drawing recruits and mounting attacks on foreign embassies and other targets.