Although there are fewer migrants camping along the Belarus side of the EU's eastern border, Polish border guards say attempts at illegally crossing into the bloc are becoming more aggressive.
Hundreds of migrants have again tried to cross the border from Belarus into Poland, despite signs of the crisis easing after migrants left a makeshift encampment.
Polish border guards said on Friday there were attempted crossings by two groups on what is the eastern border of the European Union and NATO – one involving 500 migrants, some of whom threw rocks and tear gas canisters.
The border guards said they had detained 45 migrants.
"People in the largest group ... threw rocks and someone also hurled tear gas at Polish officials. At the same time the Belarusian personnel were using lasers to blind them," said Border guard spokesperson Anna Michalska.
She said four Polish soldiers had sustained injuries that did not require hospitalisation.
Michalska said there were fewer attempted breaches at the border compared to last month, but the more recent ones "have become more aggressive".
Hundreds of Iraqis flew back home on Thursday from Belarus after abandoning their hopes of reaching the EU.
Still, many migrants remained in a heated warehouse that Belarus recently made available near the border. They had been camping in a cold and wet forest since November 8.
READ MORE: Belarus: 2,000 refugees in logistics centre
'Pushbacks must end'
The Council of Europe human rights commissioner Dunja Mijatovic called the humanitarian situation along the border "alarming" and demanded an end to Poland's controversial returns of migrants back to Belarus.
"I have personally listened to the appalling accounts of extreme suffering from desperate people ... who spent weeks or even months in squalid and extreme conditions in the cold and wet woods due to these pushbacks," she said in a statement after a four-day mission to Poland.
"All pushbacks must end immediately."
She also called on Poland to allow rights activists and media "immediate and unimpeded access to all areas along the border".
The EU and US this week announced fresh sanctions on the Belarusian regime, which has crushed political opposition and independent media since a disputed presidential election last year.
Polish media say at least 11 migrants have died since the crisis began over the summer.
The West accuses Belarus of artificially creating a crisis by bringing in would-be migrants and taking them to the border with promises of an easy crossing into the EU.
Belarus has denied this and urged the EU to take them in.