June 25 (Reuters) - Governments and humanitarian organizations worldwide have begun sending cash, rescue teams and other forms of aid to Venezuela after two powerful earthquakes on Wednesday killed at least 188 people and left more than 1,500 injured, with casualties expected to rise. The back-to-back quakes, measuring 7.2 and 7.5 in magnitude and striking roughly 160 km (100 miles) west of the capital Caracas, damaged at least 250 buildings and left, at the most recent tally, about 200 people trapped in debris. U.N.