A Ministry of Foreign Affairs and Trade spokesman said British consular staff were providing assistance to the two New Zealanders on behalf of New Zealand.
"The crew of the vessel are being provided with legal representation by Greenpeace. The New Zealand Embassy in Moscow has been advised that the New Zealanders are well and have access to basic supplies."
The spokesman said British consular representatives had attended the court hearings to observe proceedings. He confirmed the New Zealanders had been given two months' pre-trial detention.
Greenpeace has criticised the court's ruling as illegal, pointing to the fact that no charges had been laid against their campaigners.
"We will not be intimidated, we will appeal these detentions, and together we will prevail," Greenpeace international executive director Kumi Naidoo said.
Human rights group Amnesty International said it was "disturbing" that the activists had been detained without charge.
Amnesty's New Zealand executive director, Grant Bayldon, said they should be released on fair and reasonable bail, informed promptly of any charges and given full access to defence lawyers.
He said possible piracy charges were "manifestly unfounded".
Amnesty was also concerned by reports the activists were provided with inadequate interpretation during the hearings.
Mr Bayldon said the detention was another example of the continuing crackdown on the rights to freedom of expression and assembly in Russia.
"There is a long list of cases where Russia has arbitrarily restricted the right to freedom of assembly and imposed harsh sentencing on peaceful protesters."
This week, Amnesty highlighted that a member of the punk band Pussy Riot was moved to solitary confinement after she complained about prison conditions.
Reports of unfair trials in the country were numerous and widespread, and new laws allowed authorities to crack down on activist groups, Amnesty said.
