Border residents say thousands of Ethiopian troops have crossed into Somalia to join a large-scale offensive against al-Shabab extremists.

The offensive comes after a truck bombing in Somalia's capital last month killed more than 350 people. Somalia's president has visited countries in the region to seek more military support.

Abdullahi Yusuf, an elder in Luq town, says Ethiopian troops in tanks and armored vehicles passed through Thursday morning toward southwestern Somalia.

Muhummed Muse, a resident of Dolow town, also told The Associated Press that dozens of armored vehicles carrying Ethiopian troops have passed through.

Ethiopia's foreign minister confirms that troops have crossed into Somalia.

Somalia is preparing for an offensive with African Union forces meant to push al-Shabab fighters out of their strongholds in Lower Shabelle and Middle Shabelle regions.