"Relations between India and Nepal are like those of twin-siblings. Jeopardising such relations for petty electoral gains in Bihar? Tragic," party general secretary Sitaram Yechury Yechury said on micro-blogging site Twitter.
Prime Minister Narendra Modi had yesterday expressed "shock" over the killing of a youth from Raxaul in Bihar in police firing in Nepal.
The Left parties have been accusing the Modi government of straining ties with Nepal after the Himalayan nation adopted its first democratic Constitution a few weeks ago.
