TOKYO -- Japan ratified a free trade accord with the Association of Southeast Asian Nations on Saturday as the country's divided parliament ended its session.

Under the deal, about 90 percent of trade between Asia's largest economy and the 10-nation ASEAN bloc, which has a combined population of 550 million, will be tariff-free within 10 years.

The government plans to exchange diplomatic documents on the pact with ASEAN member states which have already ratified it, officials said.

The pact was automatically ratified at midnight as it remained pending in the upper house for 30 days after approval by the more powerful lower house.

The lower house, dominated by the ruling Liberal Democratic Party, voted for the accord on May 22. But legislation has been held up in the opposition-controlled upper house.

The government had extended the parliament session by six days as the ruling coalition wanted to win approval for key bills including the free trade accord with ASEAN.

Under the constitution, international treaties signed by the government are automatically ratified if the upper house does not make a decision within 30 days after approval by the lower house.

A comprehensive economic partnership agreement, the core of which is the free trade accord, was signed in April by Malaysia, the last of the ASEAN members to sign off on it.

It will be the first multinational free trade agreement for Japan, which also has been seeking to conclude a flurry of bilateral pacts amid a breakdown in global trade negotiations.

Tokyo has reached bilateral deals with eight nations, six of which are in the ASEAN group -- Brunei, Indonesia, Malaysia, the Philippines, Singapore and Thailand. The others are Chile and Mexico.