"The Secretary-General is deeply concerned about the developments in Jenin," said his spokesman Farhan Haq in a statement.
"He affirms that all military operations must be conducted with full respect for international humanitarian law," said the statement.
Earlier, Haq opted not to condemn the Israeli attacks, instead called for restraint from the parties.
"We want all attacks that hit residential areas, highly populated areas of any sort, to stop," said Haq.
"Israel is able to carry out security operations, it has to do so in such a way that avoids civilian casualties and destruction of civilian infrastructure," said the spokesman in response to repeated questions seeking a UN condemnation.
Earlier in the day, Tor Wennesland, UN Special Coordinator for the Middle East Peace Process, said on Twitter the escalating tension is very dangerous regarding the Israeli raid.
"The operation comes after months of growing tension that once again reminds us of the extremely volatile & unpredictable situation across the occupied West Bank. All must ensure the civilian population is protected," Wennesland tweeted.
Noting that he is in contact with all parties, Wennesland emphasized the need "to urgently de-escalate the situation & ensure humanitarian access and delivery of necessary medical and other supplies into #Jenin."
Israeli attack on Jenin

Nine Palestinians were killed by Israeli army fire in the occupied West Bank early Monday, including eight in Jenin, according to the Health Ministry. At least 50 other Palestinians were injured.
Tensions have been running high across the occupied West Bank in recent months amid repeated Israeli raids into Palestinian towns.
Nearly 190 Palestinians have been killed by Israeli forces since the start of this year, according to the Health Ministry. At least 25 Israelis have also been killed in separate attacks during the same period.