William Hague has rejected Muammar Gaddafi's claim that western leaders are conspiring against him.
The foreign secretary's comments came during a defiant speech from the Libyan leader in which he pledged to die as a "martyr" before surrendering power.
Col Gaddafi called on his supporters to take to the streets tomorrow, even as he pledged that his army and police would crush opposition.
"I am a warrior, I am one of the people who staged the war to give some sort of dignity to our nation," he said, in a lengthy stream-of-consciousness speech.
"Muammar Gaddafi is not an ordinary person to kill or poison. Where have you been, you rats, cats and doggies?
"I'm going to die here and die here as a martyr."
He called western leaders he claimed were plotting against him "cockroaches" and insisted real power in Libya rested in people's councils.
Speaking in the Foreign Office, Mr Hague said: "He is saying he believes there is a conspiracy of world leaders against him. There is no conspiracy - it is his own people who are rising up against him."
Outside Downing Street, protesters gathered to demand more international action against Col Gaddafi's regime.
"A few years back we were in this place protesting about what Blair was doing cosying up to Gaddafi," human rights activist Fathi Elmehdwi told politics.co.uk.
The UN security council is currently meeting in closed session to discuss its response to events in Libya, where armed forces have been deployed to crush unarmed protesters demanding Col Gaddafi's resignation.
Britain will condemn the violence and call on all parties to respect human rights and act with restraint and in accordance with international law, the Foreign Office said.
It will also raise Libya in the UN human rights council in Geneva.
"The UK will continue to be active on every diplomatic front to address the deepening crisis in Libya, in close coordination with the US, EU and countries of the region," Mr Hague said.
One former Libyan jihadist told politics.co.uk that he wanted to see the UN establish a no-fly zone over Libya to prevent Col Gaddafi using fighter jets to crush civilian resistance to his rule.
Noman Benotman of the thinktank Quilliam said he also supported a land-based intervention from UN forces.
Mr Benotman praised British prime minister David Cameron for offering the UK's support, saying his rhetoric made a big difference to ordinary Libyans.
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"I know that for many these are days of anxiety as well as days of hope," Mr Cameron said.
"Anxieties about the risks that come with change... for sure, the path will be an uneven one. But a sober assessment of the risks need not mean succumbing to pessimism. There is a more hopeful way."
Britain's hardline approach could complicate its efforts to ensure the evacuation of UK nationals currently on Libyan soil escape the country.
Landing clearances for a special chartered flight are currently being sought while HMS Cumberland, a Royal Navy frigate, is being moved to international waters off the Libyan coast to assist if required.
"I call on the Libyan authorities to protect the safety of all foreign nationals and provide necessary assistance to the British government," Mr Hague said.
In Tripoli, Col Gaddafi's diatribe continued with him reiterating his refusal to budge in the face of international criticism.
"Libya is a tree and we have watered this tree with our blood. In the shadow of this tree we will take shelter and remain," he added.