China is sending another four oil rigs to the South China Sea, state media and authorities said Friday, as Beijing and Hanoi trade accusations over an increasingly heated territorial row.

The move marks a fresh escalation of the dispute that erupted after China deployed the giant Haiyang Shiyou 981 rig seven weeks ago into waters Hanoi claims.

The row has seen a wave of deadly anti-Chinese riots in Vietnam as well as accusations from both sides of ramming by the other's vessels.

Talks in Hanoi between Chinese State Councillor Yang Jiechi and Vietnamese Foreign Minister and Prime Minister Nguyen Tan Dung over the dispute ended in deadlock on Wednesday.

One of the new rigs, Nanhai 9, was dispatched that same day and was to arrive Friday, according to a statement posted online Wednesday by the China Maritime Safety Administration.

The three other rigs -- Nanhai 2, 4 and 5 -- have already arrived at their destinations and will conduct drilling operations over the next four to eight weeks, the administration said.

Some of the positions it gave for them are east of Hong Kong and far from any area claimed by Vietnam, but it remains unclear whether the others will be deployed in disputed waters.

Chinese foreign ministry spokeswoman Hua Chunying said Friday that the rigs' operations would take place "in coastal waters of China's Guangdong and Hainan provinces" at the southern tip of the country.

"I think if anyone wants to do something at the doorstep of their house others should not read too much into that," she said, describing the rigs' activities as "normal operations".

General Nguyen Quang Dam of Vietnam's Marine Police told the country's state-run Thanh Nien newspaper that the Nanhai 9 was heading for a position "in the same area where China installed some rigs around five years ago, which are still operating now".

"We are closely monitoring the situation and have already prepared measures to deal with the different scenarios that could happen," he said.

- Riot deaths -

In a report Friday on the dispatch of the rigs, China's state-run Global Times newspaper noted that about 90 percent of China's foreign trade is conducted by sea.

"China must not only have the power to safeguard these waters but also develop the maritime economy," it said.

Relations between China and Vietnam have plummeted over the oil rig row, with Beijing saying last week that Vietnamese ships have rammed its vessels more than 1,500 times since early last month.

Vietnam has released footage showing a large Chinese ship near the Haiyang Shiyou 981 rig chasing and ramming one of its fishing boats, which then sank.

Hanoi has demanded that China withdraw that drilling platform, which is in waters near the Paracel Islands claimed by Vietnam.

Anti-Chinese riots sparked by Beijing's dispatch of the deep-sea rig claimed three Chinese lives in Vietnam last month, according to Hanoi. Beijing says four Chinese citizens died.

The dispute is only the latest between China and its southeast Asian neighbours, which challenge Beijing's expansive claims to the South China Sea.

The Philippines on Thursday asked a UN tribunal to speed up its ruling on whether China's claims in the region are in violation of international maritime law. Beijing has resolutely refused to participate in the proceedings.

Beijing has also been accused of undertaking land reclamation projects in disputed areas, further stoking tensions.