Aung San Suu Kyi has called for calm after an MP in her opposition party was wounded by a sword while canvassing in Yangon before the general election in Myanmar.

Naing Ngan Linn, a sitting MP for the National League for Democracy, suffered injuries to his head and arms when he attacked late on Thursday as his campaign group toured Tharketa township in his constituency.

The NLD urged its members to focus their campaigns with “continued momentum” as the party prepares to contest nationwide elections for the first time in a quarter of a century on 8 November.

“We call on all NLD members around the country not to respond in any way to the violence in Tharketa to ensure that the coming elections pass peacefully,” the party’s election committee said in a statement.

Naing Ngan Linn and another party member continued to receive treatment late on Friday at Yangon general hospital, where they were visited by Suu Kyi and other party officials who have called the assault the worst incident of the campaign.

Political tensions are high in former junta-run Myanmar, with the opposition likely to make major gains in the vote, potentially tipping the balance of power away from the military and its ruling party allies for the first time in generations.

Witnesses described a terrifying attack on members of the NLD by a man brandishing a sword who appeared drunk.

“Naing Ngan Linn tried to stop him ... that’s why he sustained many injuries,” said Thet Htar Nwe Win, another NLD candidate, who witnessed the incident. He said several other unarmed men attacked the group but it was not clear what motivated the violence. New Win said at least two people had been arrested.

Khin Sandar Win, the injured MP’s wife, said he suffered wounds on his forehead, hands and wrists and had undergone an operation on Thursday. His condition was not life threatening.

“It happened in front of my eyes. The man who attacked was shouting abusive words against NLD when our vehicle arrived,” she said.

Myanmar’s elections are set to crown more than four years of reforms that have seen the nation open its doors to the world under a quasi-civilian regime that replaced junta rule in 2011.

Campaigning has largely been calm, although the NLD has complained that its rivals have used religion as a political tool – concerns that carry weight in a nation that has seen waves of anti-Muslim violence in recent years.

The attack comes just days before Suu Kyi is due to speak at a major rally in Yangon on Sunday to end weeks of energetic campaigning around the country by the veteran activist.

A party spokesman who was overseeing preparations at the rally site on Friday said there would be “normal” security for Sunday’s event.