American troops have clashed with insurgents in Iraq. They began exchanging fire after a US military base was attacked in Ramadi, west of Baghdad. Meanwhile a woman and her two sons were killed when a bomb exploded outside their home in the Iraqi capital.And there was more bloody evidence of the sectarian violence which is gripping the country last night. A truck bomb went off outside a Shi’ite mosque in north-eastern Baghdad, killing at least 10 people and wounding 38 others. It happened as worshippers were leaving after evening prayers. Funerals in which emotions spilled over have already been held. Over a thousand Iraqi civilians died last month in attacks and bombings that have fuelled fears the country’s slipping towards civil war.