The visit is "prompted by UNRWA's deepening concerns for the safety and protection of some 18,000 Palestinian and Syrian civilians, including 3,500 children" still in the camp, the agency said in a statement.
On April 1, IS launched an assault on Yarmuk, Syria's largest refugee camp that lies just seven kilometres (four miles) from central Damascus.
Armed Palestinian factions have fought back and Syria's air force has struck IS positions in the camp.
Syria's regime said a military operation would be necessary to drive out IS.
Such an operation was initially supported by Palestinian factions in Syria, but later rejected by the Palestine Liberation Organisation.
Krahenbuhl is due to meet displaced refugees on Sunday at a school near the camp.
Also in Damascus, the UNRWA chief is to meet deputy special envoy Ramzy Ezzeldin Ramzy, sent on Friday by UN chief Ban Ki-moon who has warned of a "massacre" in the camp.
Since 2012, Yarmuk has been the scene of clashes between regime forces and Syrian rebels, with Palestinian factions divided and fighting on both sides.
The sprawling district, once home to 160,000 Palestinians as well as Syrians, has also endured a suffocating army siege since 2013.
- Refuge in schools -
According to Palestinian sources, some 2,500 of the remaining civilians have now taken refuge in Damascus schools.
"I don't have the strength to walk any more," said Umm Mohammed, a woman in her 70s, in a video distributed to media organisations by an activist, Rami el-Sayyed.
"I haven't left my house for fear of it being looted. But if they open the road, I don't want to stay any more," she said.
"We left Palestine and we're still suffering. What did the Palestinians do to deserve all this?"
In fighting south of Damascus, meanwhile, 35 people were killed as pro-government forces repelled an attack on a key military airport by IS-affiliated militants, a monitoring group said.
The Syrian Observatory for Human Rights said the attack targeted the outskirts of Khalkhalah military airport in Sweida province on Friday.
Syria's official news agency SANA said the army had "blocked attempts from IS terrorists to infiltrate" areas near the airport.
Khalkhalah lies along a major highway between Damascus and the regime-held city of Sweida, a stronghold of the Druze minority that has largely avoided the bloodshed of Syria's war.
The attack on Khalkhalah was the first by IS, but the airport has been previously targeted by rebels and Syria's Al-Qaeda affiliate, Al-Nusra Front.
In the northern city of Aleppo, at least 10 civilians were killed in rebel shelling of a Christian district and 10 others in regime bombardment of an area under rebel control, according to the Observatory.
More than 215,000 people have been killed in Syria's four-year war, which is increasingly dominated by jihadist groups.
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On April 1, IS launched an assault on Yarmuk, Syria's largest refugee camp that lies just seven kilometres (four miles) from central Damascus.
Armed Palestinian factions have fought back and Syria's air force has struck IS positions in the camp.
Syria's regime said a military operation would be necessary to drive out IS.
Such an operation was initially supported by Palestinian factions in Syria, but later rejected by the Palestine Liberation Organisation.
Krahenbuhl is due to meet displaced refugees on Sunday at a school near the camp.
Also in Damascus, the UNRWA chief is to meet deputy special envoy Ramzy Ezzeldin Ramzy, sent on Friday by UN chief Ban Ki-moon who has warned of a "massacre" in the camp.
Since 2012, Yarmuk has been the scene of clashes between regime forces and Syrian rebels, with Palestinian factions divided and fighting on both sides.
The sprawling district, once home to 160,000 Palestinians as well as Syrians, has also endured a suffocating army siege since 2013.
- Refuge in schools -
According to Palestinian sources, some 2,500 of the remaining civilians have now taken refuge in Damascus schools.
"I don't have the strength to walk any more," said Umm Mohammed, a woman in her 70s, in a video distributed to media organisations by an activist, Rami el-Sayyed.
"I haven't left my house for fear of it being looted. But if they open the road, I don't want to stay any more," she said.
"We left Palestine and we're still suffering. What did the Palestinians do to deserve all this?"
In fighting south of Damascus, meanwhile, 35 people were killed as pro-government forces repelled an attack on a key military airport by IS-affiliated militants, a monitoring group said.
The Syrian Observatory for Human Rights said the attack targeted the outskirts of Khalkhalah military airport in Sweida province on Friday.
Syria's official news agency SANA said the army had "blocked attempts from IS terrorists to infiltrate" areas near the airport.
Khalkhalah lies along a major highway between Damascus and the regime-held city of Sweida, a stronghold of the Druze minority that has largely avoided the bloodshed of Syria's war.
The attack on Khalkhalah was the first by IS, but the airport has been previously targeted by rebels and Syria's Al-Qaeda affiliate, Al-Nusra Front.
In the northern city of Aleppo, at least 10 civilians were killed in rebel shelling of a Christian district and 10 others in regime bombardment of an area under rebel control, according to the Observatory.
More than 215,000 people have been killed in Syria's four-year war, which is increasingly dominated by jihadist groups.
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