The searches come at a very awkward moment for Zelensky and his closest ally, with US Army Secretary Dan Driscoll due to arrive in Kyiv by the end of this week as US President Donald Trump pushes ahead with a draft peace plan. US officials are heading to Moscow next week.
One of the main sticking points for Ukraine is Russia's demand for Ukraine to hand over the territory it still controls in the eastern Donetsk region. "If they don't withdraw, we'll achieve this by force of arms," Vladimir Putin said on Thursday.
Yermak, who wields enormous influence at the top of government in Kyiv, underlined his leading role in the negotiations when he told The Atlantic website hours before news of the searches emerged that "as long as Zelensky is president, no-one should count on us giving up territory. He will not sign away territory".
However, Putin has been emboldened by minor territorial gains by Russian forces, claiming their offensive "is practically impossible to hold back".
Meanwhile, Zelensky's own position has been weakened by the domestic corruption scandal, and Russia's president has long questioned his legitimacy as leader.
The corruption scandal has rocked Ukraine this month, with investigators linking several leading public figures to an alleged $100m (£75m) embezzlement scandal in the energy sector.
The two anti-corruption agencies, Nabu and Sap, said they had uncovered an extensive scheme to take kickbacks and influence state-owned companies including state nuclear energy firm Enerhoatom.
Domestically, the corruption inquiry probe is being welcomed, but internationally it leaves Ukraine's negotiating position in a potentially perilous state.