President Jiang Zemin arrives in Vietnam today for a three-day visit amid concern that border clashes could threaten territorial agreements between the two countries. China signed two treaties with Vietnam in 1999 and 2000 demarcating their common land border and in Beibu Bay. New border posts were erected in December. Nationalist hardliners within the Vietnamese armed forces, government critics, and some affected provinces in Vietnam, were angry about the accord's land concessions and felt they undermined their interests. Local authorities on both sides of the border have ignored the accord, prompting a series of frontier clashes. One of Mr Jiang's missions during the trip will be to use his meetings with both Vietnamese Communist Party General-Secretary Nong Duc Manh and Mr Manh's predecessor, Le Kha Phieu, to seek progress and further mutual understanding in reinforcing the implementation of the two territorial agreements. Leaders on both sides do not want to see local defiance ruin the pacts, said Professor Yu Xiang, of the China Institute of Contemporary International Relations, a research institute which serves the State Council. Mr Jiang and Mr Manh were likely to agree to put pressure on local authorities to honour the agreements, he said. Mr Jiang will also brief Vietnamese party leaders on China's preparation for this autumn's 16th Party Congress, during which a key leadership reshuffle is expected. Vice-President Hu Jintao attended the Vietnamese Communist Party's Ninth Party Congress in Hanoi last April. 'The briefings and regular visits by leaders symbolise the close ties between the two communist parties. Vietnam is expected to send a senior-level party delegation to attend China's party congress,' said Professor Yu. Despite Sino-Vietnamese ties and communist solidarity, the two countries have serious differences. These include a territorial dispute over the Spratly islands. But both sides have agreed to set aside their claims and concentrate on trade links.