A Kenyan court on Wednesday granted police 15 days to hold and interrogate a man who is suspected of carrying out surveillance on President Uhuru Kenyatta's rural home in preparation for an attack.

Prosecutor Daniel Karuri told a court Wednesday that police require more time to interrogate Said Mire Siyad, who was found in the presidents home in Gatundu South in central Kenya.

Karuri said time is needed to extract mobile phone data from the suspect's phone.

"The respondent is believed to have been sent to the presidential resident to carry out surveillance for a terrorist attack," the prosecutor said.

Preliminary investigations show the suspect has other associates who are yet to be arrested, Karuri said.

Kenya security forces have increased the frequency of arrests of people suspected of involvement in extremism since four gunmen from the Somali extremist group al-Shabab killed 148 people earlier this month at a college in Garissa, Kenya.

Siyad was among eight other suspects arrested for alleged links to extremism who police presented in court Wednesday to ask for more time to investigate them.

Human rights activists have accused police of making mass arrests without evidence each time an extremist attack occurs. Most of the suspects arrested in the mass sweeps are usually released by courts due to lack evidence.

Al-Shabab militants from Somalia have vowed to carry out attack in Kenya for deploying its troops to Somalia to fight the militant Islamic group.