John Kerry, the US secretary of state, has warned the Syrian regime and its main military backer Russia to respect "frayed" ceasefire and said that its "patience was not infinite" amid mounting death toll. "Russia needs to understand that our patience is not infinite, in fact it is very limited with whether or not [Bashar] al-Assad is going to be held accountable," Kerry said on Wednesday after meeting with his Iranian counterpart Mohammad Javad Zarif in the Norwegian capital, Oslo. Kerry, who also met defence ministers from Syria, Iran and Russia in an effort to halt the fighting, particularly in the northern city of Aleppo, where raging battle has claimed dozens of lives in the past two days. "We also are prepared to hold accountable members of the opposition" who have been involved in continuing violence, he said. The Syrian conflict has drawn in world powers, with the US, along with regional powers, largely backing the moderate rebels while Russia began military offensive in support of the Assad regime in September.