An Iranian military official warned the Saudi-led coalition Tuesday that any attempts to block an Iranian cargo ship bound for Yemen with humanitarian aid will “spark a fire.” The comments come amid concerns from the United States and Saudi Arabia that the ship might be used to supply weapons to the Houthi rebels during the temporary ceasefire.

"I bluntly declare that the self-restraint of Islamic Republic of Iran is not limitless," General Masoud Jazayeri told Iran's Arabic-language Al-Alam state TV late Tuesday, according to the Associated Press. "Both Saudi Arabia and its novice rulers, as well as the Americans and others, should be mindful that if they cause trouble for the Islamic Republic with regard to sending humanitarian aid to regional countries, it will spark a fire, the putting out of which would definitely be out of their hands."

Iran reportedly said that the ship, which departed on Monday, is carrying food, medicine, tents and other supplies, as well as aid workers and reporters to Yemen’s port city of Hodeida, where it is set to arrive next week. Iran’s navy said it would provide a military escort for the ship, and U.S. officials reportedly said they were aware of at least one other vessel headed for Yemen.

However, Saudi Brigadier-General Ahmed Asiri said Tuesday that no ship would be permitted to reach Yemen unless it received the authorization of the Saudi-led military coalition in the area, the AP reported. He said that if Iran wished to deliver humanitarian supplies, it should go through the official channels of the United Nations.

The Iranian ship is headed to Yemen under the aegis of a five-day humanitarian ceasefire to deliver relief supplies to Yemen’s civilians, who have suffered in the ongoing chaos and violence in the country. A Saudi-led coalition has launched strikes against the country in an effort to oust the Shiite Houthi rebels who overthrew the government of internationally recognized President Abed Rabbo Mansour Hadi. The Houthis are believed to be supported by Iran, but both parties have denied the claims. 

Iran’s actions surrounding the aid mission have led to worries that the vessel may be used to resupply and rearm the Houthis. U.S. Army Colonel Steve Warren said that the Iranian ships were being monitored, and cautioned Tehran against “planning some sort of stunt,” the AP reported. He criticized the military escort for the civilian ship and called for the supplies to be delivered to Djibouti, where the U.N. is coordinating a humanitarian response.

The ceasefire began on Tuesday, and is set to last five days, but there have been scattered reports of fighting and at least one airstrike in the port city of Aden, the New York Times reported.

Aid workers and international groups have warned that the country’s infrastructure and health services have been severely strained due to the conflict, and its citizens have suffered from shortages of food, water, medicine and electricity. The ongoing conflict in Yemen has killed over 1,400 people, most of them civilians, according to the U.N.