* Intelligence officer says Egyptian, Kenyans killed
* Residents heard warplanes overhead before explosion
* Rebels seized in Mogadishu house raids (Recasts, adds new quotes, colour)
By Abdi Sheikh
MOGADISHU, Feb 24 (Reuters) - A missile strike killed four foreign Islamist militants south of Somalia's capital on Friday, an intelligence official said, a day after the country's prime minister called for foreign air strikes against the al Shabaab rebel group.
Residents reported hearing a large explosion which targeted a car in the early hours of the morning in an area known as 'Kilometre 60', between Mogadishu and the port town of Marka in the insurgent-controlled Lower Shabelle region.
"A very senior Egyptian was killed. Three Kenyans and a Somali also died," a senior intelligence officer who declined to be named told Reuters.
The al Qaeda-backed militants confirmed a missile strike in Kilometre 60 on a website but said it was not clear if the dead were its fighters or civilians.
Somalis in central and southern Somalia regularly report drones and warplanes flying overhead. While the United States never comments officially on drone strikes in Somalia, Washington has authorised covert operations in the Horn of Africa nation in the past.
At a London conference on Thursday aimed at energising attempts to end more than 20 years of anarchy in Somalia, U.S. Secretary of State Hillary Clinton said air strikes on areas of Somalia controlled by al Shabaab would "not be a good idea".
She said she had no reason to believe anyone was contemplating them.
One civilian said fighter jets roared overhead before a loud blast ripped through the night air.
"First we saw a huge flash and then a big explosion shook the ground," said a resident, who gave his name as Hassan. "Later we saw a huge crater and nearby trees were burned."
Al Shabaab is the most powerful of an array of militias spawned by the conflict in Somalia, where armed groups have a history of wrecking attempted political settlements and perpetuating war, instability and famine.
They are, though, on the back-foot, ousted from Mogadishu last year under military pressure and now losing territory to Kenyan and Ethiopian forces in the south. Financial troubles and divisions have weakened the group, security analysts say.
Kenya, which sent troops across the border in October and has launched a campaign of air strikes on rebel strongholds in southern Somalia, denied it carried out the attack.
The Somali government says in the past five years hundreds of foreign fighters have joined the Islamist insurgency from Afghanistan, Pakistan and the Gulf region, as well as Western nations such as the United States and Britain.
Somali authorities on Friday seized 25 suspected al Shabaab members in possession of firearms and explosives during house raids in Mogadishu.
"We suspect many fighters are hiding among the population. We are searching everywhere to eliminate any al Shabaab fighters who returned to the capital," Khalif Ahmed, Mogadishu's national security chief told Reuters.
The insurgents called their withdrawal from Mogadishu in August a tactical retreat and have since stepped up suicide and bomb attacks on the coastal city. (Writing by Richard Lough; Editing by Rosalind Russell)