Eleven Colombian soldiers and a police officer were killed in a brazen ambush this week by the country’s second-largest leftist guerrilla force, known as the National Liberation Army, or ELN, dealing a major blow to hopes for government peace negotiations with the group. The death toll is one of the worst in recent years for Colombian security forces, shattering what has otherwise been a period of relative calm. The government and Colombia’s larger and more powerful FARC rebel group are in advanced stages of peace talks taking place in Cuba that would end their 50-year conflict. Spain’s prime minister vowed Tuesday to defend the country’s unity and dismissed a new proposal by two secessionist parties to have Catalonia’s regional parliament announce the beginning of a process to form a new state. In an dress carried live on national television, Prime Minister Mariano Rajoy called the proposal “an act of provocation” that was “contrary to the Constitution, the law, the feelings of the majority of Catalans and the democratic will of Spaniards.” A small medical facility run by Doctors Without Borders in the northern Yemeni province of Saada was destroyed by two Saudi-led air strikes but there were no casualties, the aid group’s chief in Yemen said Tuesday. The first strike came on Monday and hit a building housing the facility’s administration offices, according to Hassan Boucenine, who spoke from the southern port city of Aden. A February cease-fire between government and rebel forces has largely held since both sides renewed their commitment to observe the truce Sept.