Italy is to step up naval and air patrols in the southern Mediterranean to try to prevent repeats of African migrant drownings.

It comes after hundreds of migrants died in two separate disasters in little more than a week.

Italian Prime Minister Enrico Letta said at the weekend that an "air and naval package" would be put in place south of Sicily.

Tens of thousands of migrants in flimsy, overcrowded boats have made the crossing from Africa to Italy so far this year.

At least 34 people drowned on Friday when their boat overturned, according to the Italian navy.

However, with many people still unaccounted for, the true total could be as high as 200 or more.

In a separate shipwreck on 3 October, more than 350 died.

Survivors of Friday's wreck reported their vessel had been fired on as they left Libya, according to Barbara Molinario, spokeswoman for the United Nations High Commissioner for Refugees.

She said the survivors said the shots were fired by "Libyans" but it was not possible to identify them more closely.

Libyan Prime Minister Ali Zeidan denied Libyan forces were involved, but promised to investigate.

The incident underlined the chaotic conditions in Libya, the departure point for many migrant boats.

Italian officials have been increasingly worried by the uncontrolled surge in arrivals from a region also destabilised by civil war in Syria and unrest in Egypt and elsewhere.

Defence Minister Mario Mauro said: "We intend to triple our presence, in terms of both men and means in the southern Mediterranean, for a military-humanitarian mission that has been made necessary in part by the fact that Libya is currently a 'non-state'."

He told the Catholic daily Avvenire that: "We need strong action to stop these shipwrecks out to sea."

He said operational and financial details of the deployment were being worked out and could involve more patrol vessels or more powerful ships with greater surveillance capacity.

Italian media reported that unmanned drone aircraft based in Sicily could also be used to identify boats in trouble.

In addition to coastguard and frontier police vessels, the Italian navy currently has three vessels supported by four helicopters patrolling the area, and two surveillance aircraft with night vision capabilities in support.