In a letter to Singh, he said all the accused in the murder of E Manoj on September 1 would soon be brought to book.
The Kerala Chief Minister said the state police would restore peace at the earliest in Kannur district where the murder took place, a Home Ministry release said.
Chandy said the law and order in the district is normal at present.
On September 2, Singh had a telephonic conversation with Chandy and had expressed concern over the killings of political and social activists in the state.
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Manoj was killed when an unidentified gang attacked him in politically-volatile Kannur district.
The RSS activist was waylaid by the gang which threw a country-made bomb at him and then hacked him to death before fleeing, police said.
RSS-BJP leaders alleged that the CPI(M) was behind the killing and gave a call for a dawn-to-dusk hartal in the state on September 3.