BEIRUT - An unusually bloody pre-dawn raid in Aleppo prompted condemnation from the White House on Thursday which suggested that a new approach may be necessary in dealing with the ongoing Syrian conflict.Syrian security forces and students armed with knives stormed a protest march at Aleppo University earlier Thursday, activists said, killing four and rounding up 200 demonstrators demanding Syrian President Assad step down.Western powers back the 14-month revolt, but lack the appetite for the kind of military intervention seen last year in Libya.Assad has counted on support from Russia and China to block United Nations sanctions. However, Moscow and Beijing backed the ceasefire plan and Western states may hope to persuade them to agree to penalize Assad if it collapses.On Thursday, however, the head of the monitoring mission sent to Syria under the plan said the team of UN observers in the country was having a calming effect.A Reuters team in the opposition center of Homs during the day heard continuous gunfire and the occasional sound of shelling, despite a permanent presence of monitors there.Opposition figure Fayez Sara said secret police had raided the homes of his sons Bassam and Waseem on Thursday, continuing the detentions of tens of thousands since the uprising began. "I have no idea where they have been taken. Bassam is 37. Waseem is 26," said Sara.Washington accused Assad of making "no effort" to honor a three-week-old United Nations truce and warned that world powers might do more to bring change to Syria if the ceasefire plan brokered by envoy Kofi Annan failed."If the regime's intransigence continues, the international community is going to have to admit defeat and work to address the serious threat to peace and stability being perpetrated by the Assad regime," White House spokesman Jay Carney said. "Political transition is urgently needed in Syria."