Delegates will also press Yemen to push ahead with economic reforms and tackling corruption.
Some Yemeni officials have expressed concern at the prospect of foreign interference.
"What we want above all is a commitment on the development (and) the building of our capacities against radicalisation," the AFP news agency cited Abu Bakr al-Qirbi, Yemen's foreign minister, as saying on the eve of the meeting.
Mohamed Vall, Al Jazeera's correspondent in Sana'a, the Yemen's capital, said al-Qirbi would reiterate this message at the London conference.
"He will say Yemen welcomes economic assistance from the outside world, but not troops," Vall said.
"Yemen still remains deeply concerned that the country could be overrun and even occupied by foreign troops for a prolonged period of time."
Yemen is battling an independence movement in the south of the country and Houthi fighters in the north, as well as the domestic al-Qaeda affiliate, Al-Qaeda in the Arabian Peninsula.
Vall said Yemen's tribes have recently rallied behind the government in its fight against al-Qaeda.
"But any heavy-handed security crackdown on al-Qaeda that leads to civilian deaths in rural areas could turn the tide against the government - something that could limit the government’s military options against extremism," he said.
'Clandestine US operation'
In what could further inflame anti-Western sentiments in the region, the Washington Post has reported that Barack Obama, the US president, has approved secret joint military and intelligence operations with Yemeni troops.
The report, published in the US newspaper's Wednesday editions, said the operations began six weeks ago and resulted in the deaths of six regional al-Qaeda leaders.
It said Obama approved a December 24 attack against a compound where Anwar al-Awlaki, a controversial Muslim leader who holds US citizenship, was believed to be meeting al-Qaeda leaders.
"The clerics have announced that if Americans set foot on the ground here in Yemen they would give a fatwa for jihad in this country"
Mohamed Vall, Al Jazeera's correspondent
The operation involved several dozen troops from the US military's Joint Special Operations Command.
The US advisers do not take part in raids in Yemen, but help plan missions, develop tactics and provide weapons and intelligence, the Washington Post reported citing military officials.
Vall said the news of US forces already in Yemen could complicate the security situation in the country.
"Even before this news came out, Yemenis had been concerned about US intervention. This is going to make more Yemenis afraid," he said.
"The clerics have announced that if Americans set foot on the ground here in Yemen they would give a fatwa for jihad in this country.
"Imagine what is going to happen if the masses, which listen to those clerics, follow their order and announce jihad on American troops."