Azimio leader Raila Odinga's spokesperson Dennis Onyango has allegedly been arrested, ODM director of communications Philip Etale has said.
However, police say they raided the home but did not find the ODM leader.
According to Etale, Onyango's home was raided by men suspected to be the police on Wednesday and drove away with him.
The ODM official said Onyango's son said the men came with two Subarus, which they used to whisk him away in.
"Police have a few minutes ago raided the house of Raila Odinga's spokesman Dennis Onyango, along Mbagathi Way ransacked it, and arrested him. His son says they have driven off with him in two Subaru vehicles," Etale said.
Our efforts to reach Onyango did not bear fruit, as his phone was switched off.
He becomes the second of Raila's aides to be arrested after the former Prime Minister's bodyguard Maurice Ogeta.
Ogeta was taken by plain cloth officers while he drove to work on Wednesday morning before they drove him to an unknown destination.
His whereabouts remain unknown.
An official had earlier confirmed to the Star that Ogeta was among those targeted for arrest and detention.
He had been trailed to his house in Lang'ata, the official added.
The arrests come even as some Azimio leaders are reported to have gone into hiding over fears of arrest.
The leaders went into hiding on Tuesday evening and up to Wednesday they were still missing from their usual residences.
This followed reports that a number of the leaders including Embakasi East Member of Parliament Babu Owino had been detained.
Owino was detained at Jomo Kenyatta International Airport on arrival from Mombasa.
About six other Members of the County Assembly and pockets of activists including one Calvin Okoth alias Gaucho were also detained overnight.