Neither Mnangagwa nor Nelson Chamisa, the leader of the biggest opposition party, the MDC, attended the meeting but their representatives signed the agreement, which was drafted by the National Peace and Reconciliation Commission.
Police arrested a man for heckling and accusing Priscilla Chigumba, the chairwoman of the National Electoral Commission of bias in favor of the ruling party, ZANU-PF.
There are 23 candidates standing for president in the July 30 elections, the first without former president Robert Mugabe since independence in 1980.
The attack at the end of Mnangagwa's rally in Zimbabwe's second largest city, Bulawayo, on Saturday killed two of the president's security officers and was the first serious violence in the current election campaign.
No group has claimed responsibility for the explosion, which came immediately after Mnangagwa addressed a campaign rally, but there has been speculation that it could have been carried out by several different groups or individuals including the president's rivals within ZANU-PF or disgruntled supporters of former President Robert Mugabe.
The leader of the ZANU-PF Youth League Tuesday pledged Tuesday that the group would protect Mnangagwa.
"From now onwards we offer ourselves as a human shield to our president, to the leadership and to the people of Zimbabwe," said Pupurai Togarepi.
Several of Zimbabwe's previous election campaigns have been marked by violence, particularly against the opposition party, the Movement for Democratic Change (MDC).
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