Israel claims Hizbullah is rearming and has 10,000 long-range rockets and 20,000 short-range rockets in Lebanon, according to a report from Secretary-General Ban Ki-moon.
The secretary-general's report to the Security Council focused on implementation of the UN ceasefire resolution that ended the 34-day war between Israel and Hizbullah in August 2006. The resolution reiterates a call for the disarming of all militias and bans arms transfers to them.
"Reports of Hizbullah rearming are a cause of great concern, posing serious challenges to the sovereignty, stability and independence of Lebanon," Mr Ban said, although his report did not confirm Israel's claim.
The UN chief reiterated his concern about Hizbullah's public statements and persistent reports pointing to breaches of a UN arms embargo, which bans weapons transfers to the militant Islamic group.
He also expressed concern at "the threats of open war against Israel" by Hizbullah leader Hassan Nasrallah. Nasrallah has accused Israel of trying to start a new war by assassinating a top Hizbullah commander and warned it would be a battle the Jewish state would lose.
Israel has denied involvement in the February 12th car bombing in Syria that killed Imad Mughniyeh.