The Israeli representatives at the UN noted that the rocket fire was a violation of Security Council Resolution 1701.
In the letter, Israel says that the rocket fire proves that the Security Council resolution which led to the end of the Second Lebanon War, is not being implemented as it should be in light of the threats on Israel and the UN peacekeepers operating in southern Lebanon.
According to the letter, Israel has been warning for months against the strengthening of the armed militias, including the Hizbullah organization, south and north of the Litani River, as well as against the ongoing smuggling of Syrian and Iranian weapons into Lebanon.
The Israeli representatives demanded that the United Nations Interim Force in Lebanon and the Lebanese government act immediately in an effort to prevent similar incidents from taking place in the future.
The letter went on to say that Monday night's attack was a warning call to the international community and Lebanon to take immediate steps in order to implement Resolution 1701.
The Israeli representatives also called for the immediate and unconditional release of kidnapped IDF soldiers Eldad Regev and Ehud Goldwasser.
The letter ended with the demand that UNIFIL take efficient steps in order to prevent the smuggling of Syrian and Iranian weapons into Lebanon through the Syrian border, the entry of radical elements into Lebanon and the disarming of all militias and armed organizations, according to the Security Council resolutions.
Meanwhile, Lebanese Prime Minister Fouad Siniora has condemned the roadside bomb attack on UN peacekeepers Tuesday.
In a phone conversation with UN Secretary-General Ban Ki-moon, Siniora stressed that the Lebanese security organizations were looking into the incident, as well as into the rocket fire on Israel overnight. Hizbullah also condemned the attack on the UNIFIL troops.
Barak: Situation may deteriorate any day
Defense Minister Ehud Barak said Tuesday evening that Israel must remain alert, as "we cannot know when the situation will deteriorate."
Speaking in a meeting with local council heads, the defense minister said that two 107-milimeter diameter rockets were fired at the town of Shlomi overnight.
"They were apparently fired by a weird faction somehow related to Ahmed Jibril," Barak added.
Addressing the situation in the Gaza Strip, the defense minister said that "there are continuous and intensive operational activities from the air and from the land. The activity is extremely successful in operational terms, but nonetheless, the Qassam fire continues.
"We are also preparing a large operation in Gaza, but are not thrilled to carry it out before utilizing the other ways. If and when there is need for a wide-scale operation, we will do it, as this will be the only thing left," he promised.
Yonat Atlas contributed to this report