TRIPOLI (Reuters) - Bombardment of the Libyan capital Tripoli intensified on Friday, residents said, as the United Nations envoy called for a return to a ceasefire agreed last month and eastern forces said they shot down several drones.

Slideshow ( 4 images )

Residents said the shelling was among the heaviest since the ceasefire was agreed on Jan. 12, as artillery blasts echoed through the city centre and black smoke billowed near Mitiga airport held by the government.

The fighting, between the Libyan National Army (LNA) of eastern-based leader Khalifa Haftar and the internationally recognised Government of National Accord (GNA) based in Tripoli, came as the United Nations tried to hold peace talks in Geneva.

Speaking in the Swiss city on Friday, U.N. special representative Ghassan Salame said the past 24 hours had seen “a very serious truce violation” and called for all sides to again respect the ceasefire.

Shelling of Mitiga airport, held by the GNA, has forced a suspension of flights for hours at a time on consecutive days this week and new damage to a hangar was visible after Friday’s bombardment.

The town council of Abu Salim, a Tripoli neighbourhood also held by the GNA, posted pictures of damaged houses on Facebook, while medics evacuated some patients from a hospital near the airport.

The bombing of civilian neighbourhoods of Tripoli “may amount to war crimes”, the United Nations’ Libya mission said in a statement.

The mission also condemned an attack on Thursday that it said killed five members of a family in an area held by the LNA, which has attributed the blast to a drone strike.

The LNA is backed by Egypt and the United Arab Emirates, while the GNA is supported by Turkey and allied fighters it has brought from Syria.

Haftar began his attack on Tripoli last year in the latest round of fighting in Libya since the 2011 toppling of strongman Muammar Gaddafi.

The LNA said late on Friday that it had shot down at least six Turkish drones, showing images of tangled wreckage whose authenticity Reuters could not immediately verify.