Zimbabwe's opposition said Wednesday that 20 of its members have been killed by pro-government militias in the month following a disputed presidential election that has brought increased turmoil to the southern African nation.

The statement by the Movement for Democratic Change came on the same day as an international human rights group accused Zimbabwe's army of collaborating with militants loyal to President Robert Mugabe to violently quash an opposition movement seeking his removal from power.

The two forces have been using "terror and violence" to intimidate dissidents, including members of the Movement for Democratic Change opposition party, since elections a month ago, according to Human Rights Watch.

The New York-based organization joined other groups Wednesday to outline the connection between the country's military and "war veterans" of the 1970s bush war against a white-minority government, as some of Mugabe's supporters are called.

The organization said the army was providing weapons and vehicles to the pro-Mugabe militants, who are "collaborating with the army in unleashing a campaign of terror and violence against MDC members and supporters."

"The army and its allies — 'war-veterans' and supporters of the ruling party ZANU-PF — are intensifying their brutal grip on wide swathes of rural Zimbabwe to ensure that a possible second round of presidential elections goes their way," Georgette Gagnon, Africa director at Human Rights Watch, said in a statement Wednesday.

Reuters quoted MDC spokesman Nelson Chamisa as saying in a statement Wednesday that soldiers took part in attacks on party members.

"More and more people perceived to be MDC supporters continue to be beaten up resulting in over 20 MDC activists being killed in just one month," Chamisa said.

Officials for the government and the army were not immediately available for comment.

Mugabe is widely believed to have lost the March 29 presidential vote, which could end his 28-year rule. But it is not known whether his opponent, Morgan Tsvangirai, won enough support to prevent a run-off election, as results for the vote are being withheld.

The MDC has declared itself the winner of parliamentary elections, also held March 29, after learning that the national electoral commission's recount of 23 disputed seats found 18 of the initial results unchanged. The MDC says Tsvangirai won the presidential vote as well.

More than 60 people hospitalized

The MDC says hundreds of its supporters have been attacked, arrested and driven from their homes, particularly in rural areas, which are typically strongholds of Mugabe's Zimbabwe African National Union-Patriotic Front party, or ZANU-PF.

In three days last week, more than 60 people were hospitalized, the Zimbabwe Association of Doctors for Human Rights said.

Mugabe's party has accused the opposition of inciting the violence. Security officers arrested dozens of people at MDC headquarters last week, many of whom were using the office as a hideout from violence. All were released by Tuesday.

MDC secretary general Tendai Biti appealed to the UN Security Council on Tuesday to appoint a special envoy to investigate the violence and help resolve the election crisis. While the U.S., Britain and France supported the idea, South Africa, Russia and China were opposed, according to diplomats. No envoy was appointed.

British deputy UN ambassador Karen Pierce said UN political chief B. Lynn Pascoe had spoken of "a level of political intimidation and violence that I think many council members found quite chilling."

In her statement Wednesday, Gagnon called on the UN Security Council and the African Union to take immediate steps to end the violence.

With files from the Associated Press