The Hang Seng Index dropped 0.9 per cent to 26,242.56 as of 9.30am. On the Chinese mainland, the CSI 300 Index slid 0.4 per cent and the Shanghai Composite Index retreated 0.3 per cent.
The day before a a two-week truce with Iran was set to expire, Trump said he would extend it indefinitely. The US would refrain from fresh attacks, but would maintain its blockade of the Strait of Hormuz, a key marine corridor for global oil flows, he said.
Iran had earlier declined to participate in a second round of talks aimed at finding a resolution to the Middle East conflict.
Trump has earlier said he would not extend the ceasefire unless a deal was struck with Iran.
Elsewhere in Asia, Japan’s Nikkei 225 climbed 0.1 per cent, while South Korea’s Kospi retreated 0.9 per cent and Australia’s S&P/ASX 200 lost 1 per cent.