NAIROBI, Kenya (AP) — A Tanzanian opposition leader says police have arrested several opposition figures and sealed off areas where a peaceful demonstration was to begin Monday morning over last week’s election that they call too flawed to stand.

Emmanuel Mvula, campaign manager with the ACT Wazalendo party, told The Associated Press “there is heavy deployment of security forces” in the commercial hub of Dar es Salaam, where the two main opposition parties planned to march to the national electoral commission.

The chair of the CHADEMA opposition party, Freeman Mbowe, was among those arrested overnight, Mvula said. The arrest also was reported by Robert Amsterdam, lawyer for CHADEMA's presidential candidate, Tundu Lissu.

Those arrested are accused of organizing illegal demonstrations, Mvula said. “If you ask for permission (to protest), they tell you ‘No,’” he added.

The ACT Wazalendo and CHADEMA parties have accused Tanzania's ruling party of a “butchering of democracy” after the commission declared populist President John Magufuli the landslide winner of a second term. The ruling Chama Cha Mapinduzi party also won almost all parliament seats, enough to change the constitution.

Police had warned that stern measures would be taken against anyone who tried to take to the streets.

The opposition has alleged widespread irregularities before and during the vote in the East African nation that some observers say has taken a sharp turn away from democratic ideals in the past five years. Allegations include the rejection of thousands of election observers, a massive slowdown in internet and text-messaging services and deadly violence. Few independent observers were allowed.

The national electoral commission in its announcement late Friday called all votes legitimate. Magufuli on Sunday noted “a few challenges” during the election but called it generally peaceful.

Magufuli also said this will be “my second and last term in office," notable because some ruling party officials have discussed changing the constitution of extending the presidency's term limits.

The arrests have affected Monday's demonstrations but the opposition still hopes to have them underway later in the day, Mvula said. Meanwhile, the ACT Wazalendo party has told its members not to go to police even if they are summoned, he said: “They have not dared to.”