The security service, MI5, is winding up its organised crime unit to devote more resources to preventing international terrorism.
Dame Eliza said there was an 'unprecedented level' of casework
MI5 investigations into drug trafficking and large-scale fraud will now be carried out by the newly-formed Serious Organised Crime Agency.
MI5 had an "unprecedented level" of casework, its director general said.
The announcement has been timed to coincide with publication of the reports into the London bombings.
It is hoped it will reinforce the message that counter-terrorism is MI5's top priority.
MI5 has been assisting in operations to tackle serious and organised crime for ten years.
At one stage, before the 11 September attacks, serious crime took up about 15% of its resources, with investigations into drugs, illegal immigration, arms trafficking and excise fraud.
But since then, the focus of MI5's work has shifted to countering the threat from al-Qaeda and associated groups.
Director General Dame Eliza Manningham-Buller said all serious crime investigations would be suspended to free up resources.
The service's contribution to serious crime investigations with law enforcement agencies has "been highly valued and demand for the service's assistance has always exceeded our capacity to supply it," she said.
"However, we are now faced by an unprecedented level of priority casework on international terrorism and I have decided, with the Home Secretary's agreement, that we need to withdraw from serious crime casework," she said.
"The resources freed up will help to reinforce our work on international terrorism."