Washington (CNN) Actor and director Ben Stiller appeared on Capitol Hill on Wednesday to testify on behalf of Syrian refugees as rescue workers and humanitarian groups warn of intensifying bombing raids and violence by Russian and Assad regime forces in northwestern areas of the country.

Stiller, now a goodwill ambassador for the United Nations High Commissioner for Refugees, recounted his visits to refugee camps in Lebanon and Jordan, especially decrying how the conflict had affected children.

He recalled meeting one 13-year-old boy from Aleppo in a Jordanian refugee camp who was working 12- to 13-hour days in an auto body shop because rules forbid the adults from working.

Stiller described the boy's "very war-weary face, beautiful green eyes."

" 'You work very hard for a young boy,' " Stiller recounted saying to the boy, named Khalil. "And he said, 'I'm not a boy. I'm a young man.' I think that's the reality."

'Very dire'

Raed Saleh, the head of the Syria Civil Defense -- a group of volunteers who conduct medical evacuations, do search and rescue work after bombings and provide other services to civilians caught in the conflict -- warned that the conditions that have propelled families and kids like Khalil into refugee camps are not letting up.

"The situation on the ground is very dire," Saleh told reporters this week in Washington. "There is significant suffering in civilian areas, heavy shelling targeting civilian areas, targeted by the Russians."

David Miliband, president of the International Rescue Committee, speaking with Stiller before the Senate Foreign Relations Committee, said violence is escalating and echoed Saleh's charge about Russia, saying that about 3,500 people had been displaced "in the last 36 hours" and 15 air raids and attacks had taken place "today."

"In the last 24 hours ... bombing raids by Syria and Russia continue to cause misery," Miliband said.

Syrian refugee children play during a sand storm at the Zaatari refugee camp on November 13, 2017. Some 80,000 Syrian refugees living in the Zaatari camp will have access to 14 hours of electricity per day instead of eight hours, thanks to the opening of the new solar power station. / AFP PHOTO / KHALIL MAZRAAWI (Photo credit should read KHALIL MAZRAAWI/AFP/Getty Images)

Miliband was speaking to lawmakers who had convened to discuss the humanitarian challenge in Syria. Committee Chairman James Risch, an Idaho Republican, noted that the US has been the single largest humanitarian donor to the Syrian crisis, providing $9.5 billion since the conflict began in March 2011.

"Now, the questions are, how do we maintain the momentum of support for these populations, and what programs provide a path to durable solutions for the Syrian people," Risch said. "Such solutions will both address the grievances that perpetuated the conflict and prevent sowing the seeds of future conflict."

More than half a million people have been killed since the Syrian war began, creating 5.7 million refugees. Nearly 3 million Syrian children, including 800,000 refugees, are out of school and at least 10,000 of them are unaccompanied, Risch recounted.

"We remain committed to doing what we can to save lives, while acknowledging that humanitarian assistance is just a Band-Aid," Risch said. "A political solution is long overdue. The United States stands with the Syrian people."

Russia's attacks

Saleh was recognized with an award from the US Holocaust Memorial Museum this week and by the Senate Foreign Relations Committee on Wednesday, with its leading Democratic senator, Robert Menendez of New Jersey, noting that Saleh's group of about 3,000 volunteers has "saved almost 100,000 lives" doing "courageous work on the ground in Syria, while being targeted by Russia."

Saleh has said Moscow continues to target his group with disinformation campaigns because the volunteers document Russia's attacks on civilians and other violations of international law. Russian media regularly report that the group has ties to terrorists, which the Russian military then uses as justification to target them.

The US State Department on Tuesday blasted Russia for targeting Saleh's group, known familiarly as the White Helmets, as well as Moscow's deliberate targeting of homes, medical facilities and camps for internally displaced refugees in a statement, saying it was "alarmed" by the recent escalation of violence in northwest Syria.

"Russia and the regime also blatantly continue to militarily target humanitarians such as White Helmets volunteers as they attempt to save victims in many of these affected communities," said spokesperson Morgan Ortagus, adding that the violence continues "to destabilize the region."

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"The violence must end," Ortagus said. "We call on all parties, including Russia and the Syrian regime, to abide by their commitments to avoid large scale military offensives, return to a de-escalation of violence in the area, and allow for unhindered humanitarian access to address the humanitarian disaster created by the ongoing violence."

Democrats on the Foreign Relations Committee noted, however, that the Trump administration has been scaling back support for stabilization efforts in Syria. Menendez noted that President Donald Trump has frozen and then terminated assistance to northeastern Syria and pulled troops, saying his "erratic" policies were "creating uncertainty" about US reliability.

And Menendez noted that "the administration has slammed the door on Syrian refugees," in part because of its so-called "Muslim ban."

Stiller decried what he said was the politicization and "demonization of what a refugee is ... refugees are fleeing danger, all of these people are not trying to come and invade our country."

"In many parts of the world, the term 'refugee' has unfortunately become politicized, despite the fact that refugees are real people with real stories," he said. "These people have lost everything."