With pressure for international action mounting after the beheading of 21 Egyptian Christians by Islamic militants at the weekend, Renzi had a long telephone conversation with al-Sisi just hours after Egyptian warplanes bombed Isis targets in Libya in retaliation for the executions.
Sisi had agreed with Renzi that the next steps should be political and diplomatic efforts through the UN, the Italian premier's office said.
"On Libya, wisdom, prudence and a sense of the situation is required," Renzi said in an interview with TG5 television.
"What is happening is very complicated. We are following events closely and with concern but there is no need to jump from total indifference to hysteria and an unreasonable reaction."
Italy has been pushing its allies to take a more proactive approach to the situation in Libya. Some of Renzi's ministers have stepped up their calls for action in recent days in reaction to the arrival of thousands of migrants who transit through Libya unhindered because of the chaos engulfing the former Italian colony.
Foreign Minister Paolo Gentiloni said on Friday that Italy was "ready to fight" as part of an international mission to combat the terrorist threat in Libya. Renzi's tone was noticeably more guarded.
"The situation in Libya has been out of control for three years, we have been saying this in every forum and will continue to do so," he said.
"If it wants to, the international community has the means to intervene. The proposal is to await the UN Security Council. The strength of the UN is clearly greater than that of the radical militias."
Italy's official position is that it stands ready to join, possibly lead, a UN peacekeeping force in Libya if the warring parties can be persuaded to cease fighting by UN special envoy Bernardino Leon. Gentiloni appeared to go beyond that formula on Friday with his "ready to fight" remarks.
The foreign minister said: "We cannot accept the idea that there's an active terrorist threat only a few hours from Italy by boat."
Italy could not afford to underestimate the possibility of an attack by Isis militants or of an Islamist mini-state being established in its backyard, Gentiloni argued.
Egypt and France on Monday called for an early meeting of the UN Security Council and the adoption of new measures against Isis in response to the murder of the Egyptians in Libya.