The U.S. and Israel are unsure of how many hostages that Hamas terrorists took on Oct. 7 are “still alive,” National Security Adviser Jake Sullivan said Sunday.Sullivan made the comments during an appearance on ABC’s “This Week.” He said the U.S. remains focused on securing the release of the nine U.S. citizens and one U.S. green card-holder believed to be in Hamas custody. He said that while Israel is classifying all 239 missing individuals as hostages of Hamas, there is no way to be sure how many of them are “still alive.””We do not know the precise number of hostages. We know the number of missing, and that’s the number the Israelis have given, but we don’t know how many of those are still alive,” Sullivan told ABC. “As far as Americans are concerned, there are nine missing American citizens as well as a missing legal permanent resident–a green card holder.”Sullivan said he will be meeting with family members of the missing Americans later this week.IDF SAYS SOLDIERS TOOK CONTROL OF HAMAS MILITARY STRONGHOLD AS ISRAEL-HAMAS WAR CONTINUES The U.S. and Israel are unsure of how many hostages that Hamas terrorists took on Oct. 7 are “still alive,” National Security Adviser Jake Sullivan said Sunday. (AP Photo/Susan Walsh)Sullivan was later asked about claims from Hamas that Israeli airstrikes have killed a number of hostages taken on Oct. 7. He responded that no claims by Hamas should be taken at face value, but also said the U.S. has no way to disprove or confirm the claim.CHRISTIAN IN ISRAEL EXPLAINS WHY HE EVACUATED HIS FAMILY, ‘HEZBOLLAH IS A MUCH GREATER FORCE THAN HAMAS’Israel has pounded northern Gaza with thousands of airstrikes and artillery shells in the weeks following the Oct. 7 massacre. The Israeli Defense Forces ground operation has now pressed into Gaza City, the largest population center in the region. Israel has pounded northern Gaza with thousands of airstrikes and artillery shells in the weeks following the Oct. 7 massacre. The Israeli Defense Forces ground operation has now pressed into Gaza City, the largest population center in the region. (AP/Abed Khaled)Hamas maintains a labyrinth of tunnels beneath the city, and Israeli officials have said many of the hostages are likely being held there.ISRAEL KILLS TOP HAMAS WEAPONS DEVELOPER, IDF SAYS Hamas maintains a labyrinth of tunnels beneath the city, and Israeli officials have said many of the hostages are likely being held there. (MENAHEM KAHANA/AFP via Getty Images)CLICK HERE TO GET THE FOX NEWS APP The Hamas-run Gaza health ministry claims Israel has killed over 11,000 Gazans since the fighting began, though the group makes no distinction between terrorists and civilians. The U.S. has rejected the ministry’s data outright. Anders Hagstrom is a reporter with Fox News Digital covering national politics and major breaking news events. Send tips to Anders.Hagstrom@Fox.com, or on Twitter: @Hagstrom_Anders.