SANAA, June 16 (Reuters) - Yemeni Shi'ite rebels said on Saturday they had accepted a ceasefire proposed by the government to end months of violent clashes that have killed hundreds in the north of the Arab country. "In response to the call ... and to prevent bloodshed, we declare a stop to violence and fighting and our commitment to the republican system and the constitution," said rebel leader Abdul-Malik al-Houthi in a statement sent to journalists. Yemen's state news agency said on Thursday government forces would stop military operations against the rebels if they laid down their arms. The rebels oppose Yemen's close alliance with the United States. Officials say the group wants to install a clerical regime.