JERUSALEM — Israel is using a visit this week by the United Nations secretary general, Antonio Guterres, to highlight concerns about what it says are Iran’s efforts to produce advanced, precision weapons in Lebanon and Syria.

“Iran is busy turning Syria into a base of military entrenchment,” Prime Minister Benjamin Netanyahu said at a news conference with Mr. Guterres on Monday, “and it wants to use Syria and Lebanon as war fronts against its declared goal to eradicate Israel.”

Mr. Netanyahu asserted that Iran “is building sites to produce precision-guided missiles toward that end in both Syria and in Lebanon.”

He added: “This is something Israel cannot accept. This is something the U.N. should not accept.”

Israel’s defense minister, Avigdor Lieberman, also spoke in his meeting with Mr. Guterres about Israel’s concerns about factories for precision weapons and what he called Iran’s repeated attempts to smuggle arms into Lebanon.