NAIROBI, Kenya (AP) — Tanzanian opposition leaders said Monday that police arrested key colleagues and charged them with “terrorism-related offenses” and sealed off areas where a peaceful protest was to begin 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 was "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.

A joint statement issued later by CHADEMA's presidential candidate, Tundu Lissu, and ACT Wazalendo leader Zitto Kabwe asserted that Mbowe and two other CHADEMA leaders now face “terrorism-related offenses, which mean that they will not be eligible for bail.”

Lissu and Kabwe added: “We believe that there have been attempts to arrest the two of us.” Lissu, the survivor of an assassination attempt in 2017 who returned from exile this year, was detained later Monday, questioned and released after a couple of hours, a CHADEMA statement said.

A party spokesman said Lissu was detained while at a building housing the embassies of Britain, Germany and the Netherlands along with the European Union delegation to Tanzania, adding that more details were to come.

The joint statement said scores of ACT Wazalendo members remain in custody in the semi-autonomous region of Zanzibar, and it called on other countries to condemn the Tanzanian government for its “tyrannical behavior" and said protest efforts will continue.

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. In the United States' latest critical statement on the vote, Secretary of State Mike Pompeo tweeted that “we are deeply concerned by reports of election irregularities, politically motivated arrests and violence during Tanzania’s elections last week. We urge authorities to fully address concerns of irregularities and will review allegations of the use of force against civilians.”

A separate U.S. statement earlier Monday warned that Washington “in coordination with our partners will consider actions including visa restrictions, as appropriate, to hold accountable those found to be responsible for human rights abuses and interference in the election process.”

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 ACT Wazalendo party has told its members not to go to police even if they are summoned, Mvula said: “They have not dared to.”