The Britain-based watchdog said that its research had detailed the use by the paramilitary Rapid Support Forces of sophisticated Chinese-made artillery and guided bombs in its war with the regular army, now in its third year.

Abu Dhabi has repeatedly denied arming the RSF, despite reports from UN experts, US politicians and international organisations.

Amnesty said its research was based on weapons used by the RSF in operations in the western region Darfur and during its loss of the capital Khartoum in March.

It did not say anything about the long-range drones used by the paramilitaries to attack army-controlled cities in the east and south in recent days.

"Sophisticated Chinese weaponry, re-exported by the United Arab Emirates, has been captured in Khartoum, as well as used in Darfur in a blatant breach of the existing UN arms embargo," Amnesty said.

It said it identified "Chinese GB50A guided bombs and 155mm AH-4 howitzers" through analysis of video footage and photos of RSF attacks.

It said "the only country in the world that has imported AH-4 howitzers from China is the UAE" in a 2019 deal, relying on data from the Stockholm International Peace Research Institute.

- Long-range drone strikes -

Amnesty's report came as the RSF pressed its long-range drone attacks on army-held cities.

On Thursday morning, drones targeted the country's main naval base just north of Port Sudan, seat of the army-backed government, as well as fuel depots in the southern city of Kosti, two sources said, speaking on condition of anonymity.

Later in the day, anti-aircraft fire also intercepted three drones that targeted the city of Tendelti, 92 kilometres to Kosti's west, a military source told AFP.

"The militia launched another drone attack on the Flamingo Naval Base north of Port Sudan," one source told AFP on condition of anonymity, referring to the RSF.

He said air defences had shot down 15 drones overnight.

Port Sudan on the Red Sea coast had been regarded as a safe haven, hosting United Nations offices and hundreds of thousands of displaced people, until drone strikes blamed on the RSF began on Sunday.

The port city is the main entry point for humanitarian aid into hunger-stricken Sudan, and UN chief Antonio Guterres warned the attacks "threaten to increase humanitarian needs and further complicate aid operations", his spokesman Stephane Dujarric said.

More than two years of war have killed tens of thousands of people and uprooted 13 million, according to UN figures.

On Tuesday, the army-backed government severed ties with the UAE, accusing it of supplying the RSF with the advanced weapons systems it has used to strike Port Sudan.

The UAE denied the allegation, adding that the internationally recognised administration "does not represent the legitimate government of Sudan".

In response, the Sudanese army-aligned foreign ministry on Thursday called the UAE's reaction "pathetic and ridiculous".

The ministry said it showed "strange disregard" for international laws and norms governing relations between states.

- 'No choice but to leave' -

Since losing nearly all of greater Khartoum to the army in March, the RSF has ramped up their use of long-range drones.

The strikes on Port Sudan have hit key facilities including the country's last functioning international airport, its largest working fuel depot and the city's main power station.

At Port Sudan's bustling main bus station, civilians were scrambling to leave.

"You can't get a ticket without booking over a day in advance now, all the buses are booked," said bus company employee Mahmoud Hussein.

Among those fleeing was Haidar Ibrahim, preparing to travel south with his family.

"The smoke is everywhere and my wife suffers from asthma," he told AFP. "We have no choice but to leave."

Many of those who had sought refuge in Port Sudan have been displaced multiple times.

The war has effectively split the country in two, with the army holding the north, east and centre, and the RSF in control of most of Darfur and parts of the south.