Sinha was addressing a press conference in New Delhi [ Images ] on Monday.
The ex-minister said the UPA government failed to take notice of developments in the neighbouring Nepal.
"When you land in Nepal, the announcement says 'Welcome to Nepal, the Gateway to China. This is a development which we should have taken notice of. If we not do so it can lead to serious consequences."
Asked if the development means that CPM leader Sitaram Yechuri is going to be back in action, Sinha said in a lighter vein, "He is conspicuous by his absence."