An explosion hit a vehicle carrying members of Kenya's paramilitary police force (GSU) on Friday in the north of the east African country, wounding three, medics and police said.

The attack is the fourth on Kenyan soil this week and comes a day after Kenyan soldiers had their first serious clash with fighters from Somalia's Islamist militant group al Shabaab in the south of the Horn of Africa nation.

Several sources said they suspected the GSU vehicle had been hit by a landmine, although the exact nature of the explosion remained to be confirmed officially.

Police and military sources said the attack happened not far from the town of Garissa, near Modika, on the road that leads to the Dadaab refugee camp and then onto the border with Somalia.

The vehicle in which the officers were travelling was extensively damaged and partly burnt after being hit by what we suspect might either be a landmine, or a bomb, a police source in the provincial headquarters, who declined to be named, told Reuters.

Police spokesman Eric Kiraithe told Reuters they suspected a landmine was behind the blast and two had been injured.

Two medical sources at the Garissa Provincial General Hospital said two of the GSU officers were in critical condition and a third had been admitted for treatment.

We have received three patients who have been injured. Two are in a serious condition with burns and fractures, said Musa Mohamed, a medical superintendent at the Garissa hospital.

(Reporting by Noor Ali in Isiolo and Humphrey Malalo in Nairobi; Editing by David Clarke)