Thousands of people have fled the Somali capital Mogadishu amid escalating fighting between government forces and opposition fighters.
Fierce street clashes have already claimed hundreds of lives and the government has called on neighbouring African countries to send troops to help it battle al-Shabaab fighters.
In a bid to contain the dealy six-week-old violence, Sharif Sheikh Ahmed, the Somali president, declared a state of emergency on Monday.
"As of today, the country is under a state of emergency," Sharif said at a press conference in Mogadishu, adding that he had taken the decision "after witnessing the intensifying violence across the country."
Two legislators have also been killed in the last two days of fighting and last week al-Shabab claimed responsiblity for the death of the country's security minister and at least 30 other people in a suicide car bomb attack.
At the weekend Sheikh Aden Mohamed Madobe, the parliament speaker, urged neighbouring countries to send troops to his country to prop up the government.
"We want them to come here within 24 hours," he said at a parliament meeting in the capital.
"We are asking the world and neighbouring countries to intervene in Somalia's situation immediately."
The African Union voiced its concern and gave its blessing to the government's appeal for foreign backing.
Those fighting the government are being led by a [former] Pakistani army general, they are burning the flag and killing people," Madobe said.
As the request was made, residents in central areas of Somalia reported seeing Ethiopian troops.
Ethiopian troops last entered the Horn of Africa country in late 2006 to support the then-government and drive out Islamic Courts Union fighters led by Sharif Ahmed, the current president.
Ahmed later joined the government after signing a UN-brokered peace deal and is now battling former allies from the al-Shabab and Hizbul-Islam groups, which have vowed to topple his government.
On Sunday, al-Shabab warned against any foreign military intervention in the Somalian conflict.
"We are sending our clear warning to the neighbouring countries. Send your troops to our holy soil if you need to take them back inside coffins," Sheikh Ali Mohamed Rage, an al-Shabab spokesman, told a news conference in Mogadishu.
"We tell you that our dogs and cats will enjoy eating the dead bodies of your boys if you try to respond to the calls of these stooges, because we wish to die in the way of Allah more than you wish to live."
More than 4,300 Ugandan and Burundian soldiers are already deployed in Somalia as part of an African Union (AU) force and are charged with protecting strategic sites such as the presidency, the port and the airport.
But the troops are not allowed to fight alongside government forces and are authorised only to retaliate if they come under direct attack.
The fighting in Mogadishu has so far forced an estimated 400,000 people to flee their homes in the city, many of them now living rough along the Afgooye corridor, about 20km south of the capital.