US envoy George Mitchell on Thursday called for a durable ceasefire in Gaza and vowed Washington would sustain an "active commitment" to achieve lasting peace in the region. "It is important to consolidate a sustainable and durable ceasefire and encourage efforts in that regard," Mitchell told reporters after holding talks with Palestinian president Mahmud Abbas in Ramallah. "Lasting peace is our objective and the United States will sustain an active commitment to two states living side by side in peace, stability and security."