The marches have been called to protest against alleged rigging in the 2013 general elections, Dawn online reported.
According to officials, parts of Islamabad have been blocked off by placing containers on the road.
Cellular phone services also remain suspended in the city, the officials said.
The developments come as the Lahore High Court has maintained that the two parties should not continue with their course of agitation and the government has begun taking steps to establish a judicial commission to investigate alleged malpractices in the 2013 polls.
Earlier, President Mamnoon Hussain hoisted the national flag at an Independence Day ceremony in the Presidency.
The president was flanked by Prime Minister Nawaz Sharif and army chief Raheel Sharif on the occasion.
During the ceremony, a one-minute silence was observed to pay tribute to soldiers who died in the ongoing Zarb-i-Azb military operation against militants in the country’s north-west.