Around 400 migrants have died in a failed bid to escape Libya and sail to Italy, survivors said, as the death toll from shipwrecks in the Mediterranean soars.
The boat was carrying an estimated 550 people in total when it capsized 24 hours after leaving the Libyan coast, Save the Children reported.
The number adds to more than 500 migrants who have already died while making the journey from Africa so far this year - up from 47 in the same period last year - as people there flee government instability and violence.
More than 8,000 migrants have been rescued from the Mediterranean in the past week alone, as the spring weather makes passage slightly safer.
Save the Children and other humanitarian groups have called on the European Union to strengthen its sea rescue operations programme, as migrant flows are expected to rise further during the summer months.
A security official says a bomb exploded at the gate of the Moroccan embassy in the Libyan capital earlier. Nobody was wounded in the bomb attack, he said.
The gate and a residential building next to the embassy were damaged, residents said. Militants claiming loyalty to Islamic State said on twitter they were responsible for the attack.
Five people were killed in the central Libyan city of Sirte in an apparent suicide bombing on Wednesday, a security source said.
Tripoli-based al-Nabaa television said the five died near the city's power station.
Several foreigners, including a Czech and an Austrian, are missing after gunmen attacked the al-Ghani oilfield in Libya this week, according to the Czech Foreign Ministry.
In a statement the ministry said: "There was a Czech citizen present at the spot, who has been missing since.
"Together with him, an Austrian citizen is unaccounted for as well as several other persons from third countries."
The ministry said a crisis committee including Prime Minister Bohuslav Sobotka and secret services had met to discuss the situation, and a foreign ministry representative would be dispatched to the region as soon as possible.
Libya's oil security forces said on Friday they had retaken control of the oilfield after militants attacked the facility, killing seven guards.
More than 30 people have been killed today in a series of car bomb explosions in the eastern Libyan city of Qubbah.
Parliamentary speaker Aguila Saleh told Al-Arabiya TV that a petrol station and a security building had been the targets of the bombs.
The State of Qatar has reportedly recalled its ambassador based in Cairo amid disputes over Egypt's decision to carry out air strikes in Libya.
According to state news agency QNA, the director of Arab affairs at the Qatari foreign ministry voiced concern at an Arab League meeting in Cairo over the decision to carry out air raids in Libya without consultation with other Arab states.
Egypt has carried out a number of air strikes after militants claiming to be alligned to Islamic State extremists beheaded 21 Egyptian Christians.
Libya has asked the United Nations Security Council to lift an arms ban so its army can equip itself to fight Islamic State militants.
The country's Foreign Minister Mohamed Dayri said: "Libya needs a decisive stance from the international community to help us build or national army's capacity.
"This would come through a lifting of the embargo on weapons so our army can receive material and weapons so as to deal with this rampant terrorism."
Currently the Libyan government is allowed to import weapons and related materiel but only with UN approva following the ban imposed in 2011.
David Cameron stressed Britain "has not abandoned Libya" after Egypt bombed Islamic State targets in the country in response to the murder of 21 Egyptian Christians.
"What we face in Libya is a very difficult situation, with far too many armed militias, without a proper government and with the growth of ungoverned space," the Prime Minister said.
"What the whole world needs to do is come together and work for Libya that has a national unity government."
Egyptian President Abdel Fattah Al-Sisi called for a United Nations resolution mandating an international coalition to intervene in Libya after its jets bombed Islamic State targets there.
"There is no other choice, taking into account the agreement of the Libyan people and government and that they call on us to act," he told France's Europe 1 radio.
Asked if Egypt would resume its own action, he said: "We need to do it again, and all of us together."
Egypt has opened a new front in the war against so-called Islamic State, bombing targets on the doorstep of Europe. It launched two waves of airstrikes on the Islamist terrorists in Libya.
It follows the mass murder of 21 Egyptian Christians on the Libyan seafront, barely 200 miles from the frontier of Europe. The Egyptian government has called on the international community to intervene in Libya.
ITV News Africa correspondent John Ray reports: