Sudan’s warring sides are complying better with a fragile ceasefire, despite reports of fierce fighting in Darfur.

The army and paramilitary Rapid Support Forces (RSF) began a seven-day truce on Monday intended to allow access to aid and services after battles since mid-April killed hundreds and created a humanitarian and refugee crisis.

The war broke out in the capital Khartoum on April 15 after disputes over plans for the RSF to be integrated into the army under an internationally backed deal to shift Sudan towards democracy following decades of conflict-ridden rule by former President Omar al-Bashir.

Some 1.3 million people have fled their homes, either across borders or within the vast nation. The health ministry has said at least 730 people have died with the Armed Conflict Location and Event Data Project putting that figure at more than 1,800.

Despite a drop in fighting, there have still been reports throughout the week of clashes, artillery fire and air raids. The truce was violated only minutes after it came into effect on Monday night.

“Although there was observed use of military aircraft and isolated gunfire in Khartoum, the situation improved from May 24 when the ceasefire monitoring mechanism detected significant breaches of the agreement,” a Saudi-US statement said.

Saudi and US representatives “cautioned the parties against further violations and implored them to improve respect for the ceasefire on May 25, which they did”, the statement added.

As civilians, aid groups and mediators pleaded for a stop to the fighting, Sudan’s defence ministry issued a call to arms.

In a statement on Friday, it called on “army pensioners … as well as all those capable of bearing arms” to head to their nearest military command unit and “arm themselves in order to protect themselves”, their families and their neighbours.

The week-long ceasefire is the latest in a series of agreements that have all been systematically violated, with the army and the RSF accusing each other of more breaches this week.

The United States and Saudi Arabia, which brokered the latest deal, reported “serious violations” since it took effect, particularly on Wednesday.

Washington has threatened sanctions for breaches detected by its “monitoring mechanism”, but has not yet targeted either side.

Increasingly desperate civilians have been waiting for brief lulls in fighting to flee or for assistance to flow through as battles have left the capital – a city of five million – with intermittent supplies of food, water and electricity.

Conditions are particularly dire in Darfur, on the western border with Chad, a region already ravaged by a brutal two-decade war that erupted in 2003. Fighting has flared in several major cities in western Sudan in recent days, according to activists, most recently overnight in el-Fasher, the capital of North Darfur state.

Zalingei and el-Geneina have had a communications blackout amid militia attacks.

Residents of Nyala said calm had returned after days of fighting, although water was still cut off.