TOKYO/SINGAPORE (Kyodo) -- Prime Minister Shinzo Abe is expected to announce at a news conference on Friday Japan's participation in negotiations on a U.S.-led Pacific region free trade agreement known as the Trans-Pacific Partnership.

A government source said Tuesday that March 15 is being considered as the date for making the announcement. Abe is believed to be hoping for presenting his plan, and gain backing for it, at a general assembly of the governing Liberal Democratic Party on Sunday.

Meanwhile, some countries engaged in TPP negotiations currently under way in Singapore have aired concern over Japan's policy of seeking exemptions to tariff elimination for items such as some farm produce after Tokyo joins the talks, a source close to the negotiations said Tuesday.

In Japan, the LDP panel on TPP measures is scheduled to draw up Wednesday night demands to the government such as measures to protect the politically sensitive domestic agricultural sector to prepare for joining the trade talks.

Some LDP lawmakers have expressed concern about, and opposition to, Japan taking part because of potential adverse impacts on domestic industries and the livelihood of citizens.

If discussions get too heated at the LDP panel, the date of announcement may be changed.

After making the announcement for participation, Japan will likely take steps to start negotiations such as seeking endorsement from the United States, Australia and New Zealand. Japan has not gained consent from these three countries among the 11 Asia-Pacific economies already participating in the negotiations.

Japan will unlikely enter into negotiations before June because the United States requires at least 90 days to secure congressional approval even if the administration endorses Japan's participation.

In Singapore, where the talks on the Trans-Pacific Partnership are held, participating countries shared the view that they should request Japan strictly adhere to what has been agreed on in the rounds of negotiations that have been held so far, according to the source close to the negotiations.

The source said Japan's participation was formally discussed at the meeting and some countries expressed concern that Japan has sounded out to some of the 11 participating countries if rice and other items may be exempted from tariff elimination.

The source said views were expressed at the meeting that Japan should enter into talks without setting preconditions.

The 11 countries are Australia, Brunei, Canada, Chile, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.

TPP in principle calls for elimination of tariffs on all trade items.

In the general election in December, the LDP pledged to stand against taking part in TPP negotiations unless exemptions to tariff eliminations are granted. The LDP won the election and Abe was elected prime minister.

In his talks with U.S. President Barack Obama in February, Abe confirmed that joining the free trade talks will not require a commitment to removing all tariffs.