Exxon Mobil said the cost of its gas export project in Papua New Guinea will soar to $19 billion from $15.7 billion due to foreign exchange impacts and delays from work stoppages and land access issues.

Exxon told venture partners in a letter published on Monday the PNG Liquified Natural Gas (LNG) project remains on schedule for start-up and delivery of the first LNG in 2014.

The plant's forecast capacity has been increased by 5 percent to 6.9 million tonnes per year, Exxon said.

Australian partner Oil Search said it expected the cost increases would be funded by 70 percent equity, 30 percent debt.

(Reporting By Jane Wardell)