War-torn Somalia remains in a "critical" state four years after a devastating famine, the U.N. warned on Monday, noting a sharp rise in those needing food aid.

"The levels of food insecurity and malnutrition are critical. Humanitarian actors and donors have prevented the situation being a lot worse than it is, but we all need to do more," U.N. aid chief for Somalia Peter de Clercq said in a statement.

Dozens have been killed in Somalia after Shebab gunmen ambushed an army convoy, officials and local elders said Thursday, the latest battles with the al-Qaida-linked insurgents.

Shebab fighters launched attacks on the army convoy near the village of Tulo-Barwao in the southwestern Gedo district of Somalia on Wednesday, a region bordering Ethiopia and Kenya, sparking intense gun battles.

At least 18 people were killed in Somalia on Saturday in two bomb attacks carried out by suspected Shebab militants in the south of the country and the capital Mogadishu, officials said.

In the first attack, a suicide bomber drove a vehicle laden with explosives into a base on the outskirts of the southern city of Kismayo, where African Union peacekeepers from Kenya as well as Somali government soldiers are stationed.

Tens of thousands of Somali refugees have fled back home from war-torn Yemen since an upsurge in fighting in March, the U.N. said Tuesday, adding to three million already in need.

The refugees, who originally fled hunger and conflict in Somalia before being caught up in war in Yemen, have largely crossed the Gulf of Aden by boat to the Horn of Africa country's northern Somaliland and Puntland regions.

War-torn Somalia will not be able to hold full elections due next year, lawmakers said Tuesday, although it remained unclear whether some kind of voting process would still be held.

The current President Hassan Sheikh Mohamud and parliament were appointed by clan elders in 2012 with foreign backers promising full democracy in 2016, signaling an end to decades of chaos and instability.

Somalia's president on Monday gave a defiant warning to Shebab insurgents a day after they killed at least 13 people in a bomb attack on a hotel that houses several diplomatic missions.

The suicide vehicle attack, the latest in a string of bomb blasts and killings in the war-torn Horn of Africa nation, came as U.S. President Barack Obama left neighboring Kenya and headed to Ethiopia, both key nations contributing troops to the African Union force battling the Al-Qaida-affiliated Shebab.

Somalia's Shebab insurgents killed at least six people Sunday in a huge car bomb attack on a heavily guarded hotel in the capital Mogadishu that is also home to several diplomatic missions, officials and witnesses said.

The suicide attack, the latest in a string of bomb blasts and killings in the war-torn Horn of Africa nation, came as U.S. President Barack Obama left neighboring Kenya and headed to Ethiopia, both key nations contributing troops to the African Union force battling the al-Qaida-affiliated group.

Somalia's Shebab insurgents assassinated a lawmaker and his guards, the president said late Saturday, hours after U.S. President Barack Obama said the Al-Qaeda affiliated militants had been "weakened".

Gunmen sprayed the car of MP Abdulahi Hussein Mohamud with gunfire as he travelled through a southern district of the capital Mogadishu earlier Saturday, killing him, his two guards and the driver.

Somali government troops backed by African Union forces on Wednesday captured the Shebab stronghold of Bardhere, one of the last key bases of the al-Qaida-affiliated Islamists, officials said.

The militants also confirmed the loss of the town, but insisted they had not been defeated and that fighting was continuing.

African Union troops in Somalia have dismissed reports they killed several civilians during fighting, saying those shot were all Al-Qaida-affiliated Shebab insurgents.

Witnesses in the southern port town of Merka said troops from the 22,000-strong AMISOM force killed at least eight civilians on Tuesday, opening fire after insurgents hurled a grenade at a passing convoy.