Gordon Brown has called for "immediate international action" to attend to the situation in Burma.
The prime minister has also urged the ruling junta regime in Ragoon to "exercise restraint" against the swelling pro-democracy protests.
Monks and nuns as well as ordinary citizens have taken to the streets of the capital to demand democracy. Mr Brown described the protests as "unprecedented."
Amid growing international concern over the Burmese regime's reaction, Mr Brown has written to Portuguese prime minister Jose Socrates - whose country holds the presidency of the EU - and UN secretary general Ban Ki-moon.
The prime minister argues the international community needs to send a clear message to Ragoon that tougher sanctions will be imposed if the regime orders a military crackdown against the protestors.
Mr Brown told Mr Socrates: "I strongly support a presidency initiative to warn the Burmese government that we are watching their behaviour and that the EU will impose tougher EU sanctions if they make the wrong choices."
And to Ban Ki-Moon, he stressed: "We need concerted international action, including the UN, to discourage violence. We need to stand together".
Mr Brown has also called on all nations with influence over Ragoon to use it to "deter violence and encourage reconciliation".
He is also supporting an urgent visit to Burma by the UN special envoy Ibrahim Gambari.
Mr Brown said the "unfolding human tragedy" in Burma, demands "immediate international action".
He added: "It is vital that the Burmese authorities exercise restraint in the face of the demonstrations and seize the opportunity to launch a process of real political reform."
Addressing the Labour conference today, foreign secretary David Miliband was forced to confront the growing unease in Burma.
Mr Miliband said the situation is now "tense" and joined the prime minister in calling for restraint from the authorities.
He said it was "brilliant" to see Aung San Suu Kyi - the democracy leader who has been under house arrest since 2003 - outside her compounds last week.
The foreign secretary added: "I think it will be a hundred times better when she takes her rightful place as the elected leader of a free and democratic Burma."