USNARZ GORNY, Poland, Aug 23 (Reuters) - Poland will build a fence along its border with Belarus and double the number of troops there, the defence minister said on Monday, to halt a flow of migrants the European Union says is being driven by Minsk in retaliation for EU sanctions. Poland and fellow EU states Lithuania and Latvia have reported sharp increases in migrants from countries such as Iraq and Afghanistan trying to cross their borders. The EU says Belarusian President Alexander Lukashenko is waging "hybrid warfare" with migrants to exert pressure on the bloc. Polish Defence Minister Mariusz Blaszczak said that a new 2.5-metre-(8.2-foot)-high solid fence would be built on the border with Belarus. At a press conference at the border Blaszczak also said the military presence there would be increased. "It is necessary to increase the number of soldiers. ... We will soon double the number of soldiers to 2,000," he said. Poland"s government has come under sharp criticism from human rights advocates over the plight of a group of migrants trapped for two weeks in the open between Polish and Belarusian border guards near the village of Usnarz Gorny. Poland says allowing the migrants to enter Polish territory would encourage further illegal migration and would also play into Lukashenko"s hands. "These are not refugees, they are economic migrants brought in by the Belarusian government," Deputy Foreign Minister Marcin Przydacz told reporters. INHUMANE Some lawyers and NGOs accuse Warsaw of treating the stranded migrants inhumanely by blocking their entry. The Polish Human Rights Ombudsman said the Border Guard had violated the Geneva Convention by not accepting verbal declarations from some of the migrants that they wanted to apply for international protection in Poland. "People were asking the border guards for protection and the border guards were pushing them back," said Piotr Bystrianin from the Ocalenie Foundation, which helps refugees. "That means they were in contact and that means they should give them the possibility to apply for protection. ... It is very simple." Mahdieh Gholami, a translator helping the Ocalenie Foundation, said that Polish troops were hampering her efforts to communicate with the migrants just across the border. "When I start to say something the soldiers turn on engines," she said. The Polish Border Guard and the army did not immediately respond to requests for comment. Lithuania said on Monday it would complete a 508-km (315-mile) fence along its border with Belarus by September next year. read more