Russia and Syria are “weaponising” migration as an aggressive strategy towards Europe, the senior Nato commander in Europe has said.
US Gen Philip Breedlove also said criminals, extremists and fighters were hiding in the flow of migrants.
Migrants are continuing to accumulate in Greece, after Macedonia stopped allowing more than a trickle through.
New figures suggest last year’s total of one million seaborne migrants could be reached this year months beforehand.
The International Organization for Migration (IOM) said nearly 129,500 migrants had arrived by sea so far in 2016, plus another 1,545 by land – and 418 had drowned or were missing.
The European Union is to announce plans to spend hundreds of millions of euros on humanitarian aid, as Greece struggles to cope with the influx.
The crisis has caused tensions to surge, with the European Commission criticising Macedonia for using tear gas on a crowd of migrants on Monday morning.
“The scenes we just saw are not our idea of managing the crisis,” said EC spokesman Margaritis Schinas.
In the “Jungle” camp of migrants at Calais, France, the demolition of the southern half of the camp continues – in what the government has termed a “humanitarian” operation but which critics say will just leave hundreds of desperate migrants without shelter in winter.
‘On the road’
Gen Breedlove is the head of the US European Command as well as Nato’s Supreme Allied Commander Europe.
He told the US Senate Armed Services Committee that the crisis was allowing Russia to use non-military means to create divisions in the Nato alliance and Europe.
Russia and Syria’s leader Bashar al-Assad, Gen Breedlove said, were “deliberately weaponising migration in an attempt to overwhelm European structures and break European resolve”.
He cited the use of barrel bombs – unguided weapons – against civilians in Syria. The only purpose of these indiscriminate attacks was to terrorise Syrian citizens and “get them on the road” to create problems for other countries, Gen Breedlove said.
Gen Breedlove added that violent extremists, fighters and criminals – including elements from the extremist Islamic State group – were in the mix of migrants.
He said he had requested more US forces be permanently based in Europe. Their numbers have dropped from a Cold War high of half a million to about 62,000 today.
The plan to be submitted by the EU’s executive body, the European Commission, means EU aid agencies would for the first time work directly with the UN and other groups inside Europe, rather than disbursing money to individual member states.
EU officials said the aid plan would allocate €300m (£233m; $325m) this year to help any EU state deal with the migration crisis. In all, €700m would be made available over three years.
However, BBC Europe correspondent Chris Morris says that even if such funding can be deployed quickly, the EU also needs to stem the flow of new arrivals. That would mean better co-operation with Turkey, he adds.
Greece has asked the European Commission for nearly €500m in assistance to help care for 100,000 asylum seekers.
European Council President Donald Tusk is due to visit Croatia and Macedonia on Wednesday before moving on for talks in both Greece and Turkey in advance of a special EU summit next Monday.