It is being described as the biggest air assault of its kind in Iraq in three years. US forces have launched a major offensive against insurgents, with Operation Swarmer coming amid mounting sectarian bloodshed and political deadlock. The aim is to root out guerrillas near Samarra, the site of a bombing attack last month on a Shi’ite shrine that unleashed a wave of inter-communal violence.More than 50 aircraft, 200 tactical vehicles and 1,500 Iraqi and US troops are involved. The offensive is due to last several days. According to American forces, early reports indicate that weapons caches have been found, containing artillery shells, explosives, bomb-making material and military uniforms. Several operations have been launched in the past against Sunni insurgents and suspected al-Qaeda fighters in the notorious Sunni triangle. The events come as wrangling in the Iraqi parliament blocks efforts to form a government.