LONDON/KUWAIT, April 6 (Reuters) - Fahad al-Rajaan, the former head of Kuwait's social security fund convicted in his home country of corruption and embezzling public money, has been arrested on behalf of the Kuwaiti authorities, London police said on Thursday.

Last year, al-Rajaan was sentenced to a 10-year prison term in absentia and an international arrest warrant was issued.

"Fahad Al-Rajaan, 68, a Kuwaiti national, appeared before Westminster Magistrates' Court on Wednesday, April 5, after being arrested on behalf of the authorities in Kuwait, where he is wanted in connection with allegations of fraud and theft," London police said in a statement.

The Westminster court handles extradition cases and Kuwait's attorney general Dherar al-Assousi told al-Qabas and al-Jarida newspapers that Britain had agreed to a Kuwaiti government request to extradite al-Rajaan.

"He was arrested and he will be extradited once the procedures are completed," al-Assoussi told al-Qabas.

Al-Rajaan faced accusations including embezzlement of public funds, betrayal of public trust and money laundering relating to when he was the head of Kuwait's Public Institution for Social Security (PIFSS).

Al-Assousi said a Swiss judge had ordered in December 2014 that $100 million in 15 bank accounts belonging to al-Rajaan be frozen, out of $390 million suspected to have been embezzled.

Kuwait's government has signed an extradition treaty with the United Kingdom but the parliaments of both countries have yet to ratify it.

"The extradition of al-Rajaan will be based on a special agreement signed between Kuwait and Britain, and his arrest warrant there was kept secret so he wouldn't leave the country, and so we succeeded," al-Assoussi said.

(Reporting by Ahmed Hagagy and Michael Holden; Editing by Andrew Bolton) ((aziz.elyaakoubi@thomsonreuters.com; +971552994086)(;))