NAYPYIDAW, Myanmar - China's increasing assertiveness in maritime disputes was at the heart of Southeast Asian regional talks Friday as diplomats began a series of meetings also expected to highlight concerns over host Myanmar's reform progress.Myanmar President Thein Sein began the Association of Southeast Asian Nations (ASEAN) foreign minister meetings with a plea for the regional bloc to strengthen its ability to push for "peaceful settlement of disputes and differences"."The current developments in the world are causing serious concern to us," he added, without giving specific examples, in a speech in the capital Naypyidaw.Recent acts by Beijing in the South China Sea, including the positioning of an oil rig in waters also claimed by Vietnam, have sparked a fresh spike in regional tensions. The sea, criss-crossed by key international shipping lanes, is thought to hold huge oil and gas deposits and is claimed almost in its entirety by China.ASEAN members Brunei, Malaysia, the Philippines and Vietnam all claim parts of the sea, while Taiwan is a sixth claimant. "We expressed serious concern over recent developments in the South China Sea, which have raised tensions in the area," an early draft statement to be discussed at the ASEAN foreign ministers' meeting said. Members hope to agree on the wording of a final statement by the end of Friday. In comments that could prove contentious among China's allies in the 10-member bloc, the draft also called for a cessation of "destabilising actions" in the disputed waters.The rig incident in May sent relations between Beijing and Hanoi plunging to their lowest point in decades and set off a wave of deadly anti-China riots in Vietnam.China, which is attending the Naypyidaw meetings as they broaden to include world powers in weekend security talks, has since removed its deep-sea rig from the waters near the Paracel Islands.Foreign ministers of Malaysia, Philippines and Vietnam met informally in Naypyidaw late Thursday to reinforce a joint stance on the South China Sea."When we coordinate, our position becomes stronger," a Southeast Asian diplomat said Friday when asked about the meeting. But it was unclear if all member states of the regional bloc would agree on the language as ASEAN operates on consensus.Southeast Asia expert Carl Thayer said China's decision to move its rig was partly a reaction to expectations of a "diplomatic offensive" from the United States at Sunday's ASEAN Regional Forum (ARF).US Secretary of State John Kerry, who is attending the meeting, is due to underline Washington's calls for a freeze in "provocative" acts in the sea.A state department official told AFP that discussions on the South China Sea were expected to be "robust", with claimants urged to act with "restraint", particularly China."The secretary is not looking for a showdown. This is not a superpower battle," he said on condition of anonymity ahead of the visit.Kerry is also expected to press Myanmar to reinforce its commitment to democratic reforms as the former pariah state heads towards landmark elections next year.The country, which began emerging from outright military rule in 2011, has been accused of backsliding on reforms in recent months, with journalists and activists arrested, while religious violence and the rise of Buddhist nationalism has also sparked concern.Thein Sein, whose government has been criticised by rights groups for not doing enough to stop anti-Muslim unrest, called for action against "extremism" in his opening address Friday, urging a "peace-loving majority" to stand up against violence. The ARF is an annual security dialogue among ASEAN foreign ministers and key partners, including Australia, China, India, Japan, South Korea, Russia and the European Union.