* Move follows border clashes over aid

* Washington sanctions officials, revokes travel visas

* Guaido visits Paraguay, Argentina seeking support

* Guaido says military support for Maduro draining away

By Lesley Wroughton and Daniela Desantis

WASHINGTON/ASUNCION, March 1 (Reuters) - 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 Argentine President Mauricio Macri in Buenos Aires, Guaido said, without providing evidence, that 80 percent of Venezuela's military nonetheless supported a change in leadership and that he would continue to seek the support of officers.

Earlier on Friday in Paraguay, he said 600 members of Venezuela's armed forces had already abandoned Maduro's government following the clashes over the aid.

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," U.S. Treasury Secretary Steven Mnuchin said in a statement.

The United States "will continue to target Maduro loyalists prolonging the suffering of the victims of this man-made humanitarian crisis," he said.

U.S. sanctions block any assets the individuals control in the United States and bars U.S. entities from doing any business or financial transactions with them.

The list includes National Guard Commander Richard Lopez and five other police and military officials based near the Colombian or Brazilian borders.

The U.S. 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."

Venezuela's Information Ministry did not immediately reply to a request for comment.