Prime Minister Manmohan Singh today cleared the uncertainty over the start of Kudankulam nuclear project declaring that the first unit will be operationalised in a couple of weeks but India and Russia did not sign any agreement for the third and fourth units of the plant.

After his talks with Russian President Dmitry Medvedev at the Kremlin, he said at a joint press interaction that the second unit of the plant will be operationsalised six months after that.

However, the two countries chose not to sign agreements for the third and fourth unit of the Russian-aided project in Kudankulam in Tamil Nadu where there has been an agitation on the issue of safety.

But the two countries today finalised the terms of reference for the Line of Credit for the third and fourth units.

Before the meeting, Russian officials were confident that the signing of agreements on third and fourth units would be done today.

Earlier, quoting Medvedev's foreign affairs aide Sergei Prikhodko, local agencies had said the agreements on construction of two more units at KNPP will be signed after the Kremlin talks.

Chief of Russian State Nuclear Cooperation 'Rosatom' Sergey Kiriyenko told reporters that the agreement for the construction of the third and fourth units were not signed.

Responding to the question when the Indian side would be ready to sign them, Kiriyenko said: "I don't know".

"Both India and Russia are very clear that there is nothing to worry about the safety of the Kudankulam nuclear project," Singh said in reply to questions.