Satellite images of new Chinese activity on disputed islands in the South China Sea have raised questions over China’s assertion that it has halted its land reclamation efforts, and threatened hopes for a smooth summit between Xi Jinping and Barack Obama in Washington next week.

The photos, cited in a report by the Center for Strategic and International Studies, reveal Beijing is building two airstrips in the Spratly Islands in addition to one, on Fiery Cross Reef, in an advanced state of construction.

In a statement this week, China’s foreign affairs ministry did not deny the activity on Subi and Mischief reefs, saying it was “completely lawful, reasonable and justified” given Beijing’s “indisputable sovereignty” over the Spratlys, which it refers to as the Nansha islands.