Two Democratic Republic of Congo activists are on hunger strike after the supreme court rejected their application for release from jail, where they have been held for more than a year without trial.

Fred Bauma and Yves Makwambala, members of the youth group Struggle for Change (Lucha), were arrested on 15 March last year in a raid by security services on a meeting in Kinshasa. The government said at the time that the group was believed to be planning an attack against “state security”.

“The case [against them] is empty,” said their lawyer, Beaupaul Mutemba. “They have no basis on which to hold them.”

Nearly 30 members of Lucha are now in prison after 18 were arrested on Tuesday in Goma during a peaceful protest calling for Bauma and Makwambala’s release. Last month, six were sentenced to six months in prison for incitement to revolt after police found them making banners that called for political change in a private home.

Lucha, part of a growing youth movement on the continent, hopes to emulate the success of Balai Citoyen in Burkina Faso, which played a key role in mobilising popular opposition to former president Blaise Compaoré, who was overthrown in October 2014 after 27 years in power.

Lucha is smaller but expanding and is the kind of spontaneous, grass-roots organisation that has been rare in Congo’s history, activists say.

“The government is sacred of us because we are calling for change and we are not like the opposition groups it is used to dealing with,” said Lucha activist Luc Nkulula.

The group has no formal leadership, no political affiliation and no official membership roll. Decisions are made collectively and the only internal structures are the cells focused on communications, strategy, ideology and funding. “We have no single leader so the government does not know how to control us,” Nkulula said.

The US, France, Belgium and the United Kingdom have all expressed concern about the increasing repression of political and civil society groups in the DRC and the detention of Lucha activists.

DRC’s justice minister, Alexis Thambwe, defended the case against Bauma and Makwambala, adding that the detention of Lucha activists was justified. “You cannot lead protests on the street without authorisation,” Thambwe said. “It risks destabilising the country.”

Lucha activists in Goma. Photograph: Tom Wilson

The DRC is rebuilding after two civil wars that ended in 2003 after killing more than five million people. President Joseph Kabila, in power since 2001, has overseen a period of relative stability and economic growth but the majority of the 75 million people continue to live in poverty.

Opposition groups say Kabila intends to delay an election scheduled for November in a bid to hold on to power. He won elections in 2006 and 2011, but is constitutionally prevented from running for a third term.

In December, Lucha joined a civil society and opposition party platform called the Front Citoyen to push for elections to be held this year, although members acknowledge that voting will not address all of the DRC’s problems. “The election is not a guarantee for change, it is an opportunity.” Nkulula said.

When Lucha was founded in 2012 the group focused on demanding basic facilities for the crowded neighbourhoods of Goma in which they lived: water, electricity, employment, security, justice.

The DRC has been one of the fastest growing economies in the world for the last five years, driven by rising commodity prices and increased exports of copper, cobalt, gold and other key materials, but growth has rarely trickled down to the population.

In the past 12 months Lucha’s campaigns have become more political but the group remains skeptical of the motivations of the opposition parties it now works alongside. “We don’t want power for power, we want power for change,” Nkulula said. Unlike other civil society organisations Lucha has so far rejected any external funding support. It says it is committed to maintaining its independence.

Tom Perriello, the American special envoy to the Great Lakes, said recently that the US was “deeply disappointed” with the sentences and remained “deeply concerned” about the outstanding charges against Bauma and Makwambala.

At midnight on Monday the pair began a hunger strike in protest against their “illegal and arbitrary detention”, said Lucha spokesperson Tresor Akili. During Tuesday’s protest Lucha activists walked peacefully through Goma city centre with their mouths gagged and hands tied in a powerful visual demonstration of their opposition to the government’s crackdown on political freedoms.

Nkulula says the group’s inspiration is Patrice Lumumba, DRC’s liberation hero who was imprisoned and killed in 1961 by rival political factions only six months after being elected as the country’s first prime minister. Lubumba was 36 when he was assassinated. Most of Lucha’s activists are still under the age of 30, he added.