Turkish police have seized 1.4kg of a radioactive material which had been due to be sold on the black market for £49million.

Four men were arrested after police searched their vehicle in a suburb of the capital Ankara and found 1,441grams of Californium following a tip-off.

Californium is a synthetic radioactive element which is reportedly used to 'kickstart nuclear reactors'.

Nuclear danger: The four men were found in possession of 1.4kg of Californium, a radioactive material they were planning on selling on the black market (stock image)

The men arrested are believed to be part of a larger criminal organisation, who were planning on selling the Californium for $72million (£49million) on the black market, Turkish broadcaster NTV reported.

At regular market value, 1.4kg of Californium could fetch $5.8 billion (£4.13bn), the Daily Sabah reports.

The suspects reportedly agreed to sell the cache of 1.441 kilograms of the element for $72 million on the black market. At regular market value, that amount could fetch $5.8 billion.

It is not known who the men were planning on selling the Californium to, but potential procurers include Iran and North Korea.

North Korea's leader Kim Jong-Un has indicated that he would halt testing of nuclear weapons during any potential talks with the U.S. - but a date for these have yet to be set.

In 2015, Iran agreed to not extend its nuclear energy programs for at least ten years, leading to most of the international sanctions being lifted.

However U.S. President Donald Trump has been critical of the deal, agreed to under his predecessor Barack Obama.

As recently as yesterday, The chair of the Senate foreign relations committee, Senator Bob Corker, predicted that Trump will pull out of the deal in May.

Californium was first synthesized at the Lawrence Berkeley National Laboratory in California in 1950, and to this day only the U.S. and Russia are known producers.

Turkish newspapers reported that the Californium found in Ankara had been smuggled into the country, and that although not source nation had been established, it may have come from Russia.

The element is used in nuclear reactors, in the oil industry and for detection of gold or silver when mining.

Israeli newspaper Haaretz reported that it 'is often used to kickstart a nuclear reactor'.