State-owned China Mobile is poised to buy an 18 percent stake in Thai telecom group True Corp valued at around $581 million, people familiar with the matter said, in Thailand's first major corporate deal since a coup last month.

True Corp, backed by billionaire Dhanin Chearavanont's Charoen Pokphand Group (CP Group), also plans to offer new shares via a rights issue on the basis of seven new shares for 10 existing shares, said a source.

The deal is part of the Thai group's long-term plan to secure a foreign partner, sources familiar with the matter told Reuters, and underscores Dhanin's strong political connections in China, the people noted.

In 2013, Dhanin's CP Group emerged as a surprise buyer for HSBC plc's $9.4 billion stake in Ping An Insurance Group Co of China. CP Group was the first multinational to invest in China's agri-business in 1979 and it was tasked with helping to modernize China's farm sector. It also operates Lotus supermarkets in Shanghai, according to the company's website.

True Corp and China Mobile declined comment.

The proposed deal comes in the middle of political turmoil in Thailand, which saw the imposition of military rule in May. The crisis has weighed on corporate deal-making, with volumes slumping 72 percent from a year ago to $648 million by the end of May, according to Thomson Reuters data.

"The deal is unusual given the country's political situation," said Mintra Ratayapas, an analyst at KK Trade Securities.

"Some foreign investors voice concerns about the situation in Thailand. But for True, it seems like the buyer is confident about the company thanks to strong connections with Dhanin," he said.