Eight Kenyan police officers have been killed when an improvised explosive device blew up their vehicle in a suspected attack by the Somalia-based militant group Al Shabab.

"We lost eight police officers in this attack," North Eastern Regional Commissioner John Otieno said on Wednesday.

"We suspect the work of Al Shabab who are now targeting security forces and passenger vehicles."

The incident took place on Tuesday in Garissa county in eastern Kenya, a region on the border with Somalia, where Al Shabab has been waging a bloody insurgency against the fragile government in Mogadishu for more than 15 years.

Kenya first sent troops into Somalia in 2011 to combat the Al Qaeda-affiliated militants and is now a major contributor of troops to an African Union military operation against the group.

But it has suffered a string of retaliatory assaults, including a bloody siege at the Westgate mall in Nairobi in 2013 that cost 67 lives and an attack on Garissa University in 2015 that killed 148 people.

Attacks continue in Somalia

In Somalia itself, Al Shabab has continued to wage deadly attacks despite a major offensive launched last August by pro-government forces, backed by the AU force known as ATMIS.

In one of the worst recent attacks, 54 Ugandan peacekeepers were killed when Al Shabab militants stormed an African Union base in Somalia on May 26, according to Uganda's President Yoweri Museveni.

And on Saturday, Somali police said six civilians were killed in a six-hour siege by the militants at a beachside hotel in Mogadishu.