PARIS (Reuters) - France said on Wednesday it would review a decades-old agreement that makes it easier for Algerian citizens to move to France unless Algeria agrees to take back those who are deported by the French authorities.

Already strained ties between Paris and Algiers have worsened further after an Algerian citizen whom France had long tried unsuccessfully to repatriate killed one person and injured three in a knife attack in the city of Mulhouse on Saturday.

"The drama in Mulhouse was possible because this Algerian citizen was under orders to leave the country and was presented for repatriation 14 times... and each time refused," Prime Minister Francois Bayrou told a news conference.

Under a 1968 pact between France and its former colony, Algerian citizens enjoy several exceptions to French immigration laws, making it easier to settle in France.

French Interior Minister Bruno Retailleau has repeatedly called for the pact to be reviewed following the Algerian authorities' refusal to take back its citizens who have been ordered to leave France under the "OQTF" (obligation to leave French territory) deportation regime.

Bayrou said Algeria's refusal to take back its citizens was "a direct attack on the agreements we have with the Algerian authorities and we will not accept it", adding that his government would take four to six weeks to review Algiers' implementation of the 1968 pact.

He said that over that period his government would present to Algeria a list of people it believes should return to their home country. He declined to say how many individuals are on the list but said it was "substantial".

"If that is not the case, the government considers that the advantages offered under (the 1968 agreement) will have to be reconsidered... There is a strong feeling that the agreement has been betrayed," Bayrou said.

Ties between Paris and Algiers have deteriorated in recent months since France recognised Morocco's sovereignty over the disputed territory of Western Sahara, which Rabat wants the international community to recognise as Moroccan.

That decision has angered Algiers, which backs the Polisario Front that is seeking an independent state.

(Reporting by Geert De Clercq)