Iran has boosted security for all its nuclear workers after one of its scientists was assassinated last week, First Vice President Mohammad Reza Rahimi said Tuesday.

"Whoever is active in the nuclear field will be put under special care," Rahimi said in remarks reported by the official IRNA news agency.

The order was given by President Mahmoud Ahmadinejad, Rahimi said.

ISNA news agency quoted the vice president as saying the additional measures were on top of ones ordered 10 months ago for Iran's nuclear scientists.

"This time around, the government ordered that anyone who is active in the nuclear field, from low levels to higher ups, be under surveillance and put under special care," Rahimi said.

Iran's police chief, Ismail Ahmadi Moghaddam, told reporters Tuesday his forces and the elite Revolutionary Guards would provide the security for nuclear personnel.

"The job has been divided between us and the Guards. Security details will be introduced for all of them, based on their importance," Mehr news agency quoted him as saying.

The new security order was given after Mostafa Ahmadi Roshan, a 32-year-old deputy director of Iran's main uranium enrichment plant, was murdered on January 11 along with his driver when assassins on a motorbike fixed a magnetic bomb to their car.

The attack was the fifth such incident targeting Iran's scientists in the past two years. Four other scientists -- three of them involved in Iran's nuclear programme -- died in the attacks, while one managed to escape with injuries.

Iranian officials say the attacks are a covert campaign by Israel and the United States.

On Monday, parliamentary speaker Ali Larijani said Iran had arrested an unspecified number of suspects over Ahmadi Roshan's killing, without giving their identities or nationalities.

However, foreign ministry spokesman Ramin Mehmanparast said on Tuesday that his ministry had not received "any credible report" of arrests.

Iran had previously announced, in December 2010, that it would step up security for its nuclear scientists following an attack the previous month.

The United States and Israel, along with other Western powers, say Iran's nuclear programme masks the development of atomic weapon capability.

Iran denies the claim, saying it seeks only civilian applications of the technology.