WASHINGTON/ESQUIPULAS, Guatemala (Reuters) – The organizer of a migrant caravan from Honduras was detained on Tuesday in Guatemala as the U.S. government threatened to withdraw aid from both countries if the flow of migrants north to the United States was not stopped. Up to 3,000 migrants, according to organizers’ estimates, crossed from Honduras into Guatemala on a trek northward, after a standoff on Monday with police in riot gear. The Honduran Foreign Ministry called on its citizens not to join the group. The government “urges the Hondurans taking part in this irregular mobilization not to be used by a movement that is clearly political,” it said. Over the border, Guatemalan police officers detained Bartolo Fuentes, a former Honduran lawmaker, from the middle of the large crowd that he and three other organizers had led from San Pedro Sula, Honduras, since Saturday. The moves followed comments by U.S. President Donald Trump that indicated his administration would halt aid if the Central American governments did not act, his latest effort to demonstrate his tough stance on immigration. The Honduran security ministry said Fuentes had been detained because he “did not comply with Guatemalan immigration rules” and would be deported back to Honduras in the coming hours. Security officials at the Honduran border with Guatemala in Agua Caliente blocked the road to prevent another much smaller group getting through, television images from the border showed. “We can’t attend to people en masse. People are going through one by one,” said police spokesman Alex Madrid, in a radio interview. Guatemala’s government said it did not have official figures for how many migrants from the caravan had already crossed the border. Adult citizens of the countries of Guatemala, Honduras, El Salvador and Nicaragua need only present national identity cards to cross each others’ borders. That rule does not apply when they reach Mexico. Honduran migrants, part of a caravan trying to reach the U.S., are seen before a new leg of their travel in Esquipulas, Guatemala October 16, 2018. REUTERS/Jorge Cabrera“NO MORE MONEY” Trump took to Twitter on Tuesday to express his annoyance at the caravan, which follows a similar event in May that ultimately led to hundreds of migrants either seeking asylum in the United States or remaining in Mexico. “The United States has strongly informed the President of Honduras that if the large Caravan of people heading to the U.S. is not stopped and brought back to Honduras, no more money or aid will be given to Honduras, effective immediately!” Trump wrote. U.S. Vice President Mike Pence drove home the point, saying he spoke to Honduran President Juan Orlando Hernandez and Guatemalan President Jimmy Morales warning them to help protect U.S. borders and adding “no more aid if it’s not stopped!” The strong words could encourage Honduras to move closer to China, amid intensified efforts by Beijing to win recognition from Central American countries aligned with Taiwan. Honduras is one of a dwindling number of countries that still have formal diplomatic ties with Taiwan, an island nation off the Chinese coast that Beijing views as a renegade province. Hernandez said last month that cuts in U.S. support for Central America would only hinder the country’s ability to stem illegal immigration. He welcomed China’s growing diplomatic presence in the region as an “opportunity.” Last week, Pence told Central American countries the United States was willing to help with economic development and investment if they did more to tackle mass migration, corruption and gang violence. GROWING GROUP The migrants in the group making its way north plan to seek refugee status in Mexico or pass through to the United States, saying they are fleeing poverty and violence. “What Trump says doesn’t interest us,” organizer Fuentes said in an interview shortly before his arrest. “These people are fleeing. These people are not tourists.” Widespread violence and poverty prompt thousands of Central Americans, mainly from El Salvador, Honduras and Guatemala, to make the arduous journey north toward Mexico and the United States in search of a better life. Trump ran for president in 2016 on promises to toughen U.S. immigration policies and build a wall along the 2,000-mile(3,220-km) border with Mexico. Slideshow (23 Images)Illegal immigration is likely to be a top issue in Nov. 6 U.S. congressional elections, when Democrats are seen as having a good chance of gaining control of the House of Representatives from Trump’s fellow Republicans. Reporting by Doina Chiacu in Washington and Jorge Cabera in Esquipulas, Guatemala; Writing by Delphine Schrank; editing by Frank Jack Daniel, Jonathan Oatis and Rosalba O’BrienOur Standards:The Thomson Reuters Trust Principles.