Gurugram, Dec 30 (IANS): A 40-year-old man has allegedly killed his 4-year-old son by giving him poison, before consuming it to end his own life, following an argument with his wife, the police said on Thursday.

He is currently undergoing treatment at a private hospital, and his condition is said to be critical.

According to the police, Rajesh alias Bholu, a resident of Judaula village in Gurugram, was under stress, and unhappy after his wife left him for another man around 20 days ago.

He had told his sister, Mitlesh, about the domestic tiff. Mitlesh consoled him after his wife left, and told her brother to pay more attention to his two sons -- 10-year-old Mohit, and 4-year-old Bharat.

Rajesh's wife, however, came back to him on Tuesday. The couple reportedly had an argument on Wednesday night following which he took the extreme step of killing his own son before trying to end his own life.

"The matter is being investigated. The action will be expedited after Rajesh recovers. If necessary, his wife will also be questioned. A case of murder was registered against Rajesh after a complaint was filed by his sister," Inspector Sunil Kumar, SHO of Farrukhnagar police station, told IANS.