The chief of a leading Venezuelan opposition party says a grenade has exploded outside its Caracas headquarters. Democratic Action leader Henry Ramos says the blast shattered windows and damaged the facade of the party offices late Saturday. No one was hurt. Assailants have targeted other opponents of President Hugo Chavez in recent weeks with tear gas canisters thrown at buildings owned by government critics. Tensions are high ahead of a Feb. 15 referendum that would end presidential term limits, letting Chavez seek re-election indefinitely. Chavez has condemned the attacks and ordered police to crack down. No suspects have been arrested.