(Refiles to identify Bystrianin as head of Ocalenie Foundation in paragraph 11)
WARSAW (Reuters) - Poland's interior minister said on Monday material related to Islamic extremism had been found in the phones of migrants crossing its border with Belarus and he called for a 60-day extension to a state of emergency along the frontier.
The European Union member state declared the emergency at the start of September over a surge in migration that Polish and EU officials blame on Belarus. But Poland's nationalist government has drawn criticism from rights groups over its treatment of migrants, five of whom have died on the frontier.
"(The situation is) extremely tense...I will apply to the Council of Ministers (cabinet) for an extension of the state of emergency by 60 days," Interior Minister Mariusz Kaminski told a news conference.
During the briefing Polish officials showed material which they said were text messages and other images linked to Islamic extremism found on some of the migrants' electronic devices.
Reuters could not independently confirm the veracity of the messages or images.
Poland's opposition and human rights groups have accused the ruling right-wing nationalist Law and Justice (PiS) party in the past of stoking prejudice against immigrants for political gain.
During the 2015 migrant crisis, the PiS leader said refugees from the Middle East could bring disease and parasites to Poland.
Most of the current migrants have come from Iraq, Afghanistan and Africa.
On Monday, Kaminski said the government was not trying to stigmatise the migrants but merely presenting evidence it had uncovered to show that some migrants crossing the border could pose a threat to national security.
He said that Polish security services had found links to extremism in 50 out of 200 migrants questioned.
Piotr Bystrianin, head of the Ocalenie Foundation refugee aid charity, said the minister showed no proof that any of the migrants posed a security threat.
"The aim was precisely to stigmatise these people, arouse fear and try to find some pseudo-reasons for maintaining the state of emergency. It's pure propaganda, turning people against refugees like in 2015...," he said.
Poland and the EU have accused Belarus of encouraging migrants from Iraq, Afghanistan and African countries to cross the EU's external borders to put pressure on the bloc over sanctions Brussels has imposed on Minsk over rights abuses.
However, the European Commission and rights groups fear that Poland is forcing migrants at the border back into Belarus, violating their right to seek asylum and putting them at greater risk.
(Reporting by Alan Charlish, Pawel Florkiewicz and Anna Wlodarczak-Semczuk; Editing by Mark Heinrich)