MELISSA BLOCK, HOST:
The increasing strength of the militant group, ISIS, is raising concerns in Israel. NPR's Emily Harris recently traveled to Israel's northern border for a view of the increasing regional instability.
EMILY HARRIS, BYLINE: From a high hill in northern Israel, General Gal Hirsh, an Israeli military reservist, points down into Lebanon.
GENERAL GAL HIRSH: The red roofs are very close to us, here - this is El-Adesa and Kafr Kela, down there - two villages and - of - Lebanese villages. The border is just this sandy road that you see down here.
HARRIS: The system is a fence, wired with electronic sensors and security cameras. Israeli troops run regular patrols, up and down the sandy road. It's much quieter now than during the 2006 war with Lebanon, when Hirsh commanded troops here. But with the militant Islamist group, Hezbollah, permanently on the other side, Hirsh refuses to call this border safe.
HIRSH: It is more peaceful. It's not safe because of the potential that was built here under these houses that you see here. They think it is secretly under the neighborhoods - under the houses here - under mosques - under schools - under civil infrastructure. They use the population as a human shelter, and they build and rebuild the infrastructure of rocket launchers, ammunition warehouses - just here, near the border.
HARRIS: Hezbollah crossed into Syria to fight on Bashar Assad's side last year. Some Israeli analysts say this has hurt the group, as it's lost key commanders. But Benedetta Berti, an expert on Hezbollah, says there is a flipside.
BENEDETTA BERTI: The organization is gaining important significant training and experience in conventional war fighting, which is something that could very much prove useful to Hezbollah in its next confrontation with Israel.
HARRIS: No one in Israel expects that soon, but perhaps after the war in Syria ends, if Hezbollah can maintain ground there. Right now, the various factions are too busy fighting each other.
HIRSH: Do you see there - the smoke there? That's a battle there.
HARRIS: I don't see it. Oh yeah, yeah, yeah.
HIRSH: Mortars and shells and - that's the area.
HARRIS: On another hilltop, less than an hour's drive away, Hirsh points out a battle in Syria. It's impossible to know who's fighting. Hirsh said it almost doesn't matter to Israel.
HIRSH: We just know that we must make sure that no one will penetrate, and no one will launch, and no one will come, and it doesn't matter what flag he holds.
HARRIS: Last week, the ISIS rebel group that has been fighting in Syria captured parts of Iraq. Yoram Schweitzer, a researcher with Israel's Institute for National Security Studies, says Israel is watching ISIS carefully.
YORAM SCHWEITZER: Especially the power image that it portrays through the entire region - this is more dangerous than its tangible achievements.
HARRIS: But what might Israel to?
ROBERT BLECHER: You know, Israel does not have an answer to jihadis.
HARRIS: Robert Blecher, Mideast expert with the International Crisis Group, says one Israeli strategy is deterrence.
BLECHER: They're going to hit the other guy harder than the other guy could ever hit them, and thereby deter them from even starting anything.
HARRIS: But he says that doesn't stop militant Islamist groups.
BLECHER: The other thing which Israel does is what the security establishment there calls mowing the grass, which means continually wiping out the kind of capacity that could actually harm Israel. That doesn't work really well with the Jihadis either.
HARRIS: Israelis are concerned that jihadi groups could be hiding among the hundreds of thousands of Syrian refugees in neighboring Jordan. Oded Eran used to be Israel's ambassador there.
ODED ERAN: There have been attempts to smuggle in - into Jordan - groups that, sometime in the future, may try to at least destabilize the monarchy and the system in Jordan. If this happens, and certainly if it is somehow successful, this would really destabilize the whole region.
HARRIS: About a thousand American military personnel are in Jordan, and Israel shares intelligence with its western neighbor. Former Ambassador Eran says Israel is also providing extra water to Jordan to help the refugee crisis and allowing port access through Israel now that trucks cannot reach the Mediterranean via Syria. For now it's eyes on the borders, not boots on the ground. Emily Harris, NPR News, Jerusalem. Transcript provided by NPR, Copyright NPR.