As hundreds of wounded civilians have been stranded in opposition-held areas of Aleppo, around 150 people rallied in central London on Saturday calling for Britain to take decisive action to end the five-year war in Syria.They piled up teddy bears outside Downing Street to symbolize the number of young casualties in the battered city of Aleppo from a recent surge in violence.They also delivered a letter to Prime Minister Theresa May's 10 Downing Street office demanding she take action to help cease the bloodshed.Demonstrators in London waved placards reading "Child murder is a war crime" and "Save Aleppo's children". They chanted: "Down with Bashar al-Assad! Down with dictators!"Bert Wander, campaign director with the activist group Avaaz, told AFP: "They could impose sanctions on relevant parts of the Russian economy -- for example, military equipment."They could also up diplomatic pressure. It's been limp, frankly, so far. There's so much more that could be done in terms of putting pressure on the Russians to back down."Wael Aleji, a spokesman for the Syrian Network for Human Rights, said: "The UK can step up efforts and push for a UN General Assembly resolution to override the Russian and Chinese veto at the UN Security Council."