HAVANA, Nov 15 (Reuters) - Cuba reopened schools and its borders to international tourism on Monday as opposition groups urged supporters to protest for greater political freedoms, setting up a tense showdown between the government and its critics on the Caribbean island. Dissidents have for months called on social media for a "Civic March for Change" following street protests in July, the largest on the island in decades. Cuba"s communist government has banned Monday"s planned demonstrations, saying they are part of a destabilization campaign by the United States, which maintains a Cold War-era embargo on Cuba. U.S. officials have denied that. Residents across the island reported no major rallies as of midday local time, but dissidents continued calls on social media to launch protests at 3 p.m. (2000 GMT) in 10 cities across Cuba, from the capital Havana to Pinar del Rio and Guantanamo. In Havana there was a notable increase of plain-clothed and uniformed police, though streets appeared quieter than normal as some parents kept their kids home. "I decided to keep my 6-year-old home from his first day at school because I was worried that something might happen," state worker Jennifer Puyol Vendesia said. Demonstrations planned on Sunday by a Facebook group called Archipielago, which has led the call for protests, fizzled out. Government supporters on Sunday surrounded the home in Havana of Yunior Garcia, a playwright and Archipielago leader. That prevented him from marching alone, as he had planned, to draw support for peaceful marches. Neither Garcia nor his wife answered their phones on Monday. Garcia"s neighborhood was quiet, and his building was still draped with Cuban flags that government supporters had hung from the rooftop the day before, according to a Reuters witness. Garcia and others had asked Cubans to clap in support of their movement Sunday afternoon, and to bang pots in the evening, but residents of Havana and several provincial cities said their neighborhoods remained quiet. Dissidents are again calling on Cubans to bang pots on Monday at 8 p.m. The timing of the protests - the same day tourism and schools are set to reopen following the pandemic - touched a nerve with the government. State security and groups of pro-government supporters staked out the homes of high-profile dissidents from early Monday, according to rights groups and reports on social media. On Monday morning, Saily Gonzalez, another Archipielago leaders, posted on Facebook a video that appeared to show government supporters gathering outside her Santa Clara home. In the video, the group, some dressed in red in support of the government, called her a traitor and warned her against marching. Gonzalez yelled back, telling them she would march despite their threats. U.S. Secretary of State Antony Blinken on Sunday condemned "intimidation tactics" by Cuba"s government ahead of the planned march and vowed Washington would seek "accountability" for the crackdown. "We call on the Cuban government to respect Cubans" rights, by allowing them to peacefully assemble... and by keeping Internet and telecommunication lines open," Blinken said in the statement. Cuban Foreign Minister Bruno Rodriguez responded on Twitter, telling the United States to stay out of Cuban affairs. Eunice Pulles, dressed in a white shirt on a Havana street to show her support for the dissident movement, said she thought most would be too intimidated by police and government supporters to join her in protest. "There will be no protests because the people are scared that we will be repressed," she said.