This week's attack just outside the UK parliament has highlighted the importance of protecting national borders and stepping up security measures, French far-right presidential candidate Marine Le Pen said on Thursday.

National Front leader Le Pen told BFM TV and RMC radio that countries had to co-operate with each other on sharing intelligence, and advocated closing down mosques with links to extremism and revoking the French nationality of those with more than one passport who were guilty of committing attacks.

"The problem we have nowadays is this form of low-cost terrorism," said Le Pen, adding "we must control our borders".

British counter-terrorism police were investigating the background of an attacker who killed four people and injured about 40 before being shot to death by police just outside the British parliament in London.

The attack injured three French high-school students, and French foreign minister Jean-Marc Ayrault said in a statement that he would be visiting London on Thursday and would meet those French victims.

Le Pen is currently registering relatively high scores in French opinion polls ahead of the presidential election in April and May, but those polls show her losing eventually to centrist candidate Emmanuel Macron.