Baku and Yerevan have accused each other of initiating the border clashes on Tuesday, which claimed the lives of more than two hundred people.
Pelosi who spoke with newsmen in in Yerevan condemned the attacks which she said threaten the prospects of the much-needed peace agreement.
She said Armenia has particular importance to the US because of the focus on security following an illegal and deadly attack by Azerbaijan on the Armenian territory.
Pelosi said the attack was an assault on the sovereignty of Armenia.
Hostilities between the Caucasus arch foes ended overnight on Thursday following a mediation by the United States after earlier attempts by Russia to broker a truce failed.
