A top Bangladesh court has ruled that the registration of the nation's biggest Islamic group as a political party was illegal, barring it from contesting next year's election and deepening concerns over growing violence.

The Dhaka High Court's verdict Thursday was in response to a 2009 petition claiming that Jamaat-e-Islami, an opponent of the current governing party, does not believe in democracy or the sovereignty of Bangladesh. Several of Jamaat's leaders have this year been sentenced to jail or death by a tribunal judging crimes during the country's war of independence four decades ago, sparking deadly unrest.

"This is the first step toward banning Jamaat from politics," State Minister for Law Qamrul Islam said after the verdict.

Violence has erupted across Bangladesh this year as the war tribunal reopened wounds that led to the founding of the country in 1971. With more verdicts expected and national elections due by January, there is a "significant risk" that Bangladesh could descend into a cycle of violence and lawlessness, Human Rights Watch said in a report Thursday.

Jamaat called on supporters to enforce a 48-hour shutdown starting Aug. 12 to protest the verdict, after the end of Ramadan.