Vice President Han Zheng did not mention the US by name in his remarks. The US has launched a pressure campaign on Cuba that has largely blocked oil from reaching the island. The US war on Iran started with US-Israeli strikes in February.
The comments stood in sharp contrast to the bonhomie on display earlier this week at the White House, where President Donald Trump feted Chinese leader Xi Jinping with military flyovers and at a lavish state dinner.
"Major countries should have special responsibilities for safeguarding international peace and security, and they should take the lead in complying with the rules, upholding rule of law, and doing what's right," Han said.
"China holds that the sovereignty and security of countries in the Middle East, including the Gulf, should be respected."
Trump warned Xi against providing support to Iran during the Washington talks and received assurances that China would not do so, the US ambassador to China said on Friday.
The warning followed reports that Beijing had supplied Iran with shoulder-fired air-defence missile launchers and that Tehran had found ways to evade sanctions on its oil sales with Chinese help.
On Cuba, Han said: "China urges the relevant country to immediately stop using threat of force against Cuba and immediately and completely lift the blockade and sanctions against Cuba."
Cuba's electrical grid suffered a total collapse earlier this month, plunging the nation into darkness and leaving millions without power as the US presses its blockade.
Cuba's aging power generation system has been under severe strain from fuel shortages and decrepit infrastructure for years, but a US-imposed oil blockade that began in January has worsened blackouts and led to frequent grid collapses.
Han also used the speech to portray China as a reliable partner on the global stage and a steadfast defender of developing nations.
"China holds that all countries, big or small, are equal members of the international community, and that world affairs should be handled by all through consultation," said Han.
