KYIV (AFP) - Residents of the northern Ukrainian town of Novoselytsya were told on Monday (March 21) to temporarily take shelter after an ammonia leak at a nearby chemical factory, amid intense fighting with Russian forces in the area.

Sumy regional governor Dmytro Zhyvytsky said there had been an "ammonia leakage" at the Sumykhimprom facility, affecting an area within 2.5km of the plant.

The extent and cause of the incident was not immediately clear and residents were told to seek refuge in basements or on lower levels of buildings to avoid exposure.

At 0745 GMT (3.45pm Singapore time), Ukrainian rescue services announced on Twitter that the incident was "finished". According to Sumykhimprom's website, the facility produces a range of chemical fertilisers.

Sumy, located about 350km east of Kyiv with a pre-war population of around 250,000, has experienced weeks of heavy fighting.

In recent days, the Russian government has intensified propaganda and disinformation efforts alleging Ukraine is preparing to use improvised chemical weapons and has been developing a clandestine WMD (weapons of mass destruction) programme.

The Russian Ministry of Defence claimed late on Sunday that "nationalists" had "mined" ammonia and chlorine storage facilities at Sumykhimprom "with the aim of mass poisoning of residents of the Sumy region, in case of entry into the city of units of the Russian Armed Forces".

Russia has repeatedly denied helping Syria use chemical weapons in multiple attacks against its own citizens during the country's 11-year-old civil war.

Moscow has also denied using chemical weapons against Russian opposition leader Alexei Navalny, as well as former Russian spy Sergei Skripal and his daughter Yulia.