But Zeidan said he expected more assistance from Europe to counter migration and asked Italy for help in reinforcing its southern land border in the Sahara where many migrants come from.
Letta and Zeidan also agreed on a programme for Italy to help train 5,000 new army and police personnel in an effort to undermine militias, which wrought havoc in Libya in recent months.
Letta said an international conference would be held in Rome before the end of the year on increasing assistance for Libya.
Italy is Libya's former colonial ruler and enjoyed close ties with dictator Muammar Qaddafi, although it then supported Nato action to depose him.
"The flux of illegal immigrants is a very high priority for us. It is important that you assist in curbing this phenomenon, which has unfortunately become uncontrollable," Letta said.
Thousands of migrants have arrived in Italy this year – a sharp increase from 2012 – and the rate of arrivals has increased sharply in recent weeks because of improving weather conditions.
Zeidan said Italy had agreed to supply Libya with military equipment, vehicles, and small arms to help boost the armed forces against militias.
On immigration, he said: "All these efforts to counter immigration require the active partnership of all the countries in the northern Mediterranean".
Thousands of economic migrants and refugees have arrived in Italy on boats from Libya since the start of the anti-Kadhafi revolution in 2011, which led to an easing of maritime border controls.