Kenya has de-registered 510 non-governmental organisations (NGOs), including 15 accused of links with terrorism, an official has said.

The government has also frozen their bank accounts and revoked the work permits of foreign employees.

The move follows a heated debate in Kenya over a controversial new security bill aimed at fighting militants.

The al-Qaeda-linked al-Shabab group has been increasingly targeting Kenya for attack.

The organisations had been de-registered because of their failure to submit financial records, said Henry Ochido, the deputy head of the government-appointed NGO Co-ordination Board, which oversees their activities.

Fifteen are suspected of financing "terrorism", Mr Ochido told the BBC.

The decision is bound to cause an uproar in Kenya, where many fear that the government is using the threat posed by al-Shabab to curb democratic freedoms, reports the BBC's Wanyama Chebusiri from the capital, Nairobi.

"The NGOs with accounting issues can only be allowed to operate if they successfully go through a thorough vetting process. Otherwise, they will remain deregistered indefinitely," Fazul Mahamed, the executive director of the board, is quoted by Kenya's privately owned Standard newspaper as saying.

Last week, Kenya's parliament passed a bill which gave security and intelligence agencies wide-ranging powers, including:

• the right to detain terror suspects for up to one year
• to tap communications without court consent
• and the requirement for journalists to obtain police permission before investigating or publishing stories on domestic terrorism and security issues.

Al-Shabab has killed 64 people in two attacks in the north-eastern Mandera region since last month.

Non-Muslims were singled out and shot dead in an attack on quarry workers and bus commuters.

Last year, 67 people were killed when four gunmen took over the Westgate shopping centre in Nairobi.

Kenya's President Uhuru Kenyatta has said the government will not "flinch" in the campaign to defeat the militants.