Prime Minister Narendra Modi with Bihar Chief Minister Nitish Kumar at a function in Patna (Press Trust of India photo)

As Prime Minister Narendra Modi and Bihar Chief Minister Nitish Kumar shared the stage in Patna, the jibes were sugar-coated. But hours later in Muzaffarpur, PM Modi's barbs at the Chief Minister, one of his sharpest critics, were far from subtle.This morning, at the launch of a railway project in Patna, Nitish Kumar said: "I have a personal request for the PM. When he was Chief Minister of Gujarat, I went to his state as railways minister. He should see to the completion of the Daniawan-Bihar Sharif rail project that should have begun much earlier."Referring to the previous BJP government led by Atal Bihari Vajpayee till 2004, Mr Kumar said: "If a decision had not been taken at the time to hold elections six months before schedule, then the project would have started in 2004."Speaking after him, PM Modi responded: "I agree with Nitish ji. The work that would have been completed during the Vajpayee government is being completed now. The rail work would have been completed if Vajpayee remained in power. He was railways minister then. I share Nitish Kumar's pain. Bihar suffered because of politics."Later in Muzaffarpur, while launching the BJP-led NDA coalition's campaign for the upcoming state polls, PM Modi tore into Nitish Kumar."Unhoney bhi chahakna shuru kiya," the prime minister remarked, referring to Nitish Kumar's relatively recent debut on Twitter.Referring to Mr Kumar's tweet mocking his visit after 14 months, PM Modi said he was "very grateful" for the welcome."There was a time (Nitish Kumar) said, why do you need to come to Bihar, don't come to Bihar. Now see how the suffering of your own makes you worried and desperate. The Chief Minister is upset that I came after 14 months. Don't worry, your suffering is over. Now, I have come."Nitish Kumar has been one of Narendra Modi's sharpest critics and severed ties with the BJP in 2013 over the projection of Mr Modi as prime ministerial candidate."You had problems with one man, so you throttled Bihar," PM Modi said.