Chinese President Xi Jinping arrives at the Shanghai Cooperation Organization (SCO) summit in Ufa, Russia. Thomson Reuters China is preparing for "high-level political dialogue" with Japan, China's top diplomat told the head of Japan's National Security Council on Thursday, fueling speculation of a leaders' summit as early as September.

Sino-Japanese ties, long bedeviled by China's memories of Japan's wartime aggression and disputed islands in the East China Sea, have improved since Japanese Prime Minister Shinzo Abe met Chinese President Xi Jinping at an Asia-Pacific summit in Beijing in November.

The two met for a second mini-summit in April at an Asia-Africa leaders' gathering in Jakarta and Japan wants to keep the thaw on track, while ensuring China realizes the risks of an increasingly assertive maritime-military policy.

"China attaches great importance to your trip and is preparing for high-level political dialogue between the two countries," State Councilor Yang Jiechi, who outranks the foreign minister, told visiting Japanese National Security Council head Shotaro Yachi, according to a media report.

Yang also told Yachi, who is a close ally of Abe's, that both countries "should promote exchanges in all aspects".

"China hopes that the two countries could step in the same direction, enhance mutual trust, uphold the principles of learning from history and preparing for the future," Yang said.

Yachi told Yang the bilateral relationship was improving and their meeting would be an important channel.

Over the weekend, Chinese state media quoted China's vice foreign minister, Cheng Guoping, as saying Xi had already invited Abe to attend events to mark the end of the World War Two.

Japanese government sources have said another Xi-Abe meeting could well take place this year, although some said China probably first wants to see a planned statement by Abe marking the 70th anniversary of the end of the war.

Abe's critics worry he wants to dilute past government apologies for Japan's wartime behavior, though he has said he will uphold them.

China is also keeping a wary eye on Abe's push for a more muscular defense policy that would ease the pacifist constitution's constraints on military activity abroad.

High-level dialogue, however, has already resumed, including Japanese Finance Minister Taro Aso's recent meeting with his Chinese counterpart.

A successful summit with Xi could bolster Abe's support at home, which has sagged over doubts about his security policy.

(Reporting by Sui-Lee Wee; Editing by Robert Birsel)