The United States on Wednesday pleaded with Sudan's army to join talks on ending the devastating war as talks opened in Switzerland with only its rival's participation.War has raged since April 2023 between the Sudanese army under the country's de facto ruler Abdel Fattah al-Burhan and the paramilitary Rapid Support Forces (RSF), led by his former deputy Mohamed Hamdan Daglo.With Burhan not showing up for the start of the talks, US Secretary of State Antony Blinken appealed directly to him by telephone to join.Blinken "reiterated the need for participation" in his call with Burhan, State Department spokesman Vedant Patel said.Blinken told him of the "urgent need" for both sides "to end the war and guarantee humanitarian access for the millions of Sudanese who are suffering", Patel said.Tom Perriello, the US special envoy for Sudan, said after the opening session that it was "high time for the guns to be silenced".The talks, which could last up to 10 days, are being held behind closed doors in an undisclosed location in Switzerland.While the RSF delegation is taking part, the Sudanese armed forces (SAF) are unhappy with the format arranged by Washington.Sudanese Media Minister Graham Abdelkader said ahead of the talks that the government was rejecting "any new observers or participants" -- after Washington "insisted on the participation of the United Arab Emirates as an observer".The Sudanese army has repeatedly accused the UAE of backing the RSF -- allegations the UAE denies.Humanitarian access -The talks are co-hosted by Saudi Arabia and Switzerland, with the African Union, Egypt, the United Arab Emirates and the United Nations acting as a steering group."Our focus is to move forward to achieve a cessation of hostilities, enhance humanitarian access and establish enforcement mechanisms that deliver concrete results," Perriello said.The brutal conflict has triggered one of the world's worst humanitarian crises.The fighting has forced one in five people to flee their homes, while tens of thousands have died.More than 25 million across the country -- more than half its population -- face acute hunger.Vittorio Oppizzi, Sudan programme manager for the medical charity Doctors Without Borders (MSF), said both parties had "manipulated" humanitarian access, in violation of international law.He told reporters MSF was well used to operating in conflict zones, and safe and unhindered access "should not be dependent on a cessation to hostility or a solution to the conflict".- Pressure on Burhan -Alan Boswell, the Horn of Africa project director at the International Crisis Group, said Burhan was facing "serious internal divisions", with some in his camp in favour of talks and others "fiercely opposed". Notably, with the United States in charge, and Saudi Arabia, the UAE and Egypt present, "that puts all the main outside actors with leverage over the warring parties in one room together", he told AFP.The government no-show could leave Burhan under mounting external pressure if he is seen as "the main obstacle to ending the war", said Boswell.Previous talks in the Saudi city of Jeddah came to nothing.Cameron Hudson, from the Center for Strategic and International Studies' Africa programme, told AFP that Washington had "tried to create the illusion of momentum" to force the army's hand, "but it was a bluff and the SAF saw through it.""The only way to get them to talk is through brute force: either the risk of losing the war on the battlefield, the risk of real diplomatic isolation and the risk of real economic devastation for them. None of that pressure currently exists."'Peace, now' -There has been no let-up in the fighting.The Emergency Lawyers -- a group of volunteer lawyers who have documented human rights violations during the war -- reported "increased indiscriminate artillery shelling by the RSF on civilian areas" this week, particularly in El-Fasher and Omdurman, where they reported strikes on a school, a bus carrying civilian passengers and a hospital.Around a hundred demonstrators gathered outside the UN headquarters in Geneva, chanting: "Action for Sudan" and holding a banner reading "Stop the catastrophic war"."We are not naive but this is critical now and they have to sit down and negotiate peace. We want peace now, ceasefire now," co-organiser Lina Rasheed told AFP.Amani Maghoub, who came especially from London, said: "The situation is so bad, we want the war to stop right now," adding: "We want justice for the Sudanese."