*Washington revokes visas of49 people aligned with Maduro Guaido tours South America, claims military support for Maduro draining away

The United States on Friday ramped up its attempt to dislodge Venezuelan President Nicolas Maduro from power, imposing new sanctions and revoking visas, while opposition leader Juan Guaido said Maduro's support among the military was cracking.

Venezuelan military officials last weekend blocked an opposition-backed effort to bring food into the country via its borders with Colombia and Brazil, leaving two aid trucks in flames and five people dead.

Guaido, who is recognized by most Western nations as Venezuela’s rightful leader, visited Paraguay and Argentina on Friday to shore up Latin American support for a transition government for the crisis-stricken nation.

But Maduro retains control of state institutions and the apparent loyalty of senior figures in the armed forces.

Following a meeting with ArgentinePresident Mauricio Macri in Buenos Aires, Guaido said, without providing evidence, that 80 percent of Venezuela's military nonetheless supported a change in leadership.

Foreign military intervention is seen as unlikely and Guaido's international backers are instead using a mix of sanctions and diplomacy to try to put pressure to bear on Maduro.

"We are sanctioning members of Maduro's security forces in response to the reprehensible violence, tragic deaths, and unconscionable torching of food and medicine destined for sick and starving Venezuelans," US Treasury Secretary Steven Mnuchin said in a statement.

The US State Department later said it had revoked the travel visas of 49 people as it cracked down on "individuals responsible for undermining Venezuela's democracy."