China urged calm and restraint by all sides on Monday, following U.S. President Donald Trump's threat to blockade the Strait of Hormuz after the failure of weekend talks in Islamabad aimed at ending the Iran war.

Before the war, most Iranian oil exports were shipped to China, the top global importer of crude.

Keeping the key Strait of Hormuz waterway safe, stable and unimpeded served the interest of the international community, foreign ministry spokesperson Guo Jiakun told a regular press conference, when asked about the blockade threat.

"China hopes the relevant parties will abide by the temporary ceasefire arrangements, remain committed to resolving disputes through political and diplomatic means, and avoid a resumption of hostilities," he said.

China stood ready to "play a positive and constructive role" in resolving the crisis, Guo added, calling the opening talks in the Pakistani capital a step in a direction conducive to easing tension.

After the marathon talks failed, the U.S. Central Command said its forces would begin a blockade of all maritime traffic with Iranian ports from 10 a.m. ET (1400 GMT) on Monday.

China and Pakistan had backed peace talks in March while urging an immediate ceasefire in the Iran war and restoration of normal navigation in the Strait of Hormuz, a conduit for about a fifth of global oil and gas supplies.

Guo rejected reports that China had plans to supply weapons to Iran as "groundless smears and malicious associations".

Last week, Trump threatened immediate tariffs of 50%, with no exemptions, on imports from countries supplying Iran with military ​weapons.

"China has consistently taken a prudent and responsible approach to arms exports," Guo said, adding that its strict controls were in line with domestic laws and international obligations.

-Reporting by Joe Cash; Writing by Beijing Newsroom; Editing by Clarence Fernandez/Reuters