The attacks were a shock to many in Hargeisa after years of peace
A prominent local religious leader has been arrested over multiple suicide attacks in northern Somalia.
At least 29 people were killed on Wednesday in five co-ordinated car-bombings in the autonomous Somaliland and Puntland regions.
Puntland security forces detained the Muslim cleric, Sheikh Mohamed Ismail, in a raid in the capital, Bosasso.
The BBC's Jamal Abdi in Somaliland's capital, Hargeisa, says foreign workers are being evacuated from the city.
The decision was reached after a meeting between international organisations and government officials.
Most of the casualties were in Hargeisa, where the presidential palace, Ethiopian consulate and UN offices were targeted.
In Puntland, six intelligence officers were killed in their offices after two suicide attackers struck.
Authorities in Hargeisa are following a couple of leads including the house where the bombs were assembled and the mart where the cars used were purchased, our correspondent says.
The authorities have halted an ongoing voter-registration process while they beef up security around the city.
No-one has claimed responsibility for the attacks, but the US has said it believes they were carried out by militants linked to al-Qaeda.
These were the first suicide attacks in the two relatively stable regions.
Somaliland has declared independence from war-torn southern Somalia but this has not been internationally recognised.
The region is a US ally in the fight against Islamist militants in Somalia.