Guinea-Bissau's military rulers have banned protests and strikes as they tighten control ahead of a high-level visit by West Africa's ECOWAS bloc that is seeking to restore constitutional order following last week's coup.

The military government, which seized power in what some West African leaders have termed a "sham" coup, announced late on Sunday that all demonstrations, strikes and activities regarded as threats to peace and stability were prohibited.

The directive also ordered public institutions, ministries and state secretariats to reopen and resume operations.

The announcement followed protests in Bissau on Saturday, where hundreds, primarily youths, demanded the release of detained opposition leaders and the publication of presidential election results.

The mediation team from the Economic Community of West African States (ECOWAS) - comprising the presidents of Togo, Cape Verde and Senegal, along with the ECOWAS Commission president - was expected in Bissau on Monday.

The delegation aims to persuade the coup leaders to restore constitutional order and release the contested presidential election returns.

ECOWAS has warned it may impose sanctions on individuals or groups responsible for disrupting Guinea-Bissau's electoral and democratic processes.

The interim president installed by military officers, Major-General Horta Inta-a, said the coup was necessary to ward off a plot by "narcotraffickers" to "capture Guinean democracy" and vowed to oversee a transition that would last one year, beginning immediately.

The coup reflects a continued pattern of instability in Guinea-Bissau, a major cocaine transport hub with a long history of military interventions in politics.