Juan Guaidó, the Venezuelan opposition leader, wrote in an opinion article published Wednesday evening that his opposition coalition had met with members of the powerful armed forces to galvanize support for a change in government.

Mr. Guaidó, the head of the country’s National Assembly, last week declared himself interim president in a direct challenge to Nicolás Maduro, who has held on to power despite a widely discredited election and an economic and humanitarian disaster precipitated by his government’s mismanagement.

In the days since, more than two dozen countries, including the United States and many Latin American nations, have thrown their support behind Mr. Guaidó. On Thursday, the European Parliament recognized him as the country’s legitimate leader. The American government has imposed sanctions intended to force out Mr. Maduro, but he has the support of some other nations, including Russia and China.

Ultimately, though, the fate of the two leaders may be decided by Venezuela’s military, which plays an outsize role in the country’s politics as a power broker.