Tripoli's only working airport was targeted in an airstrike on Monday, as forces loyal to renegade Libyan general Khalifa Haftar continued their advance on the capital, ignoring global calls for a truce.
She said: "The attack near Mitiga airport [on Monday] that left many civilians in Tripoli stranded brought into stark focus the imperative for all parties to respect worldwide humanitarian law, and to take all possible measures to protect civilians and civilian infrastructure, including schools, hospitals and prisons".
"In the area around the airport, civilians were terrified immediately after this air strike".
They are fighting on the southern side of the city, where witnesses said on Monday afternoon the LNA had lost control of a former airport and withdrawn down the road.
Spokesman Colonel Mohamed Gnounou said it was aimed at "purging all Libyan cities of aggressor and illegitimate forces", in reference to Haftar's fighters.
A USA amphibious hovercraft departs with evacuees from Janzur, west of Tripoli, Libya, Sunday, April 7, 2019.
Mitiga airport, in the eastern quarter of Tripoli, was shuttered after it was attacked by Haftar's so-called Libyan National Army (LNA).
In central Tripoli, while there were no signs yet of military and security vehicles or personnel on the streets, shops and cafes were closing earlier than usual in the evening and residents were apprehensive about the prospect of violence.
At least 2,800 people have so far fled fighting around Tripoli, the United Nations says.
AG Barr promises color-coded Mueller report coming next week
It is not clear, however, if Mueller's report found that Trump obstructed justice during the investigation. Barr could mollify some angst when he releases the report, even though some portions will be redacted.
Serraj has run Tripoli since 2016 as part of a UN-brokered deal boycotted by Haftar.
The death toll continues to rise in Libya, where attacks have killed more than 45 people in the last few days.
United Nations envoy Ghassan Salame met Serraj in his office in Tripoli on Monday to discuss "this critical and hard juncture", the UN's Libya mission said.
The offensive has raised fears of return to all-out war in Libya and left a question mark over the UN-led effort to lay the groundwork for elections with the 14 to 16 April conference.
Its elite force, Saiqa (Lightning), numbers some 3,500, while Haftar's sons also have well-equipped troops, LNA sources say.
Since NATO-backed rebels ousted Gaddafi, Libya has been a transit point for hundreds of thousands of migrants trekking across the Sahara in hope of reaching Europe across the sea.
France, which has close links to Haftar, said it had no prior warning of his push for Tripoli, a diplomatic source said.
Forces allied to the Tripoli government meanwhile announced their own operation called "Volcano of Anger" to defend the capital, a spokesman said, without giving details.
Hifter's forces have clashed with rival militias which support the United Nations -backed government that controls Tripoli and the western part of the country.