Britain plans to send a navy warship to help battle the smuggling of both people and arms off the coast of Libya, Prime Minister David Cameron will tell G7 leaders.

The European Union this week agreed to help rebuild Libya's shattered navy and coastguard to tackle migrant smugglers after a plea for aid from the new U.N.-backed unity government in Tripoli.

A U.N. Security Council resolution would be needed to go after arms traffickers on the high seas, ministers said at the time.

A government spokesman said that during a session on foreign affairs on Thursday evening, Cameron would set out Britain's plans to increase its involvement in the region, where it already has four ships.

"(The prime minister will) make the argument it is a global challenge requiring a comprehensive solution, reiterate our determination to work with the Libyan government and help them build the capacity of their coastguard to help them intercept boats off the Libyan coast," the spokesman said.

"We will now take an active leadership role in that process ... Once the relevant U.N. security resolutions are in place, we intend to deploy a navy warship to the region to assist in the interception of arms and human smuggling."

U.N.-backed Libyan Prime Minister Fayez Seraj, who has yet to establish his government beyond Tripoli, wrote to EU foreign policy chief Federica Mogherini to request the naval support, as well as possible training for Libyan security personnel.

A British government official said there had not yet been a formal request from Libya to operate within its waters, but one was expected "fairly swiftly." The warship could be operating in the area within weeks, the official added.

The EU's "Operation Sophia" mission operates in international waters near Libya but is too far out to destroy boats used by people smugglers, catch traffickers or head off migrants seeking to reach Europe by sea from Libya.