A politician who forced Armenia's prime minister to resign led thousands of people on a march on Tuesday after which he said he was ready to take the reins of power and would keep up pressure on the ruling elite until they agreed to real change.

Prime Minister Serzh Sarksyan, who had previously served as Armenia's president for a decade, resigned on Monday after almost two weeks of street protests prompted by accusations he had manipulated the constitution to cling to power.

Lawmaker Nikol Pashinyan played a key role in ousting Sarksyan, organising many of the protests and calling for the premier to go in a televised exchange before being jailed and then released. He had been set to start talks with the ruling party on Wednesday, but they were cancelled late on Tuesday.

"The talks are cancelled," Tigran Avinyan, Pashinyan's spokesman, told Reuters. He gave no reason and representatives of the ruling Republican Party were not immediately available for comment.

In a move likely to prolong the political crisis that has rocked one of Russia's closest allies in the former Soviet Union, Pashinyan said earlier on Tuesday he was ready to become the country's next prime minister.

"If people put this responsibility on me, I'm ready to become the prime minister," Pashinyan, wearing his trademark black baseball cap and military-style T-shirt, told reporters.

The 42-year-old said the velvet revolution he had helped bring about was not over and that the next step would be the election of a new prime minister by parliament and the holding of an early parliamentary election.

Pashinyan said he would not accept a new prime minister drawn from the ranks of the Republican Party, which Sarksyan, the man he forced to resign, still leads.

If elected himself, Pashinyan said he would try to maintain a balance in foreign policy, but ruled out challenging the presence of Russian military bases in Armenia or the country's membership in Russia-led military and economic alliances.

"We are not going to make any sharp geopolitical moves," he said.

Hours earlier, Pashinyan had led thousands of people through the capital Yerevan to a hilltop memorial dedicated to the victims of Ottoman Turk massacres of Armenians in 1915, cementing his growing political stature.

Some chanted his name and waved the national flag as they marked the anniversary of the killings.

Armenia say the killings during World War One constituted genocide. Muslim-majority Turkey accepts that many Christian Armenians were killed in fighting during the war but denies the killings amounted to genocide.

Acting prime minister Karen Karapetyan, an ally of the ousted Sarksyan, said it was important to stay united amid the political tumult.

"We are going through a very difficult stage in our new history ... demonstrating to the entire world that despite difficulties and unresolved problems we are united," Karapetyan said in a statement after laying flowers at the memorial to the victims of the massacres.

Prospects unclear

Sarksyan's allies such as Karapetyan remain in important positions in government and it remains unclear whether his resignation will herald any real change.

Armenia's political parties in parliament must put forward the name of a new prime minister within seven days.

Pashinyan has a history of political activism and was among opposition activists who demonstrated against Sarksyan's 2008 presidential election victory. Ten people were killed in clashes that followed that win.

After a period of hiding, Pashinyan surrendered to the police in 2009 and was sentenced to four years in prison for organising civil disturbances. He was released two years later under an amnesty.

"Nikol is a really popular leader whom we trust," Karen Mkhitaryan, a 19-year-old student, said of Pashinyan.

Politicians and experts said on Tuesday that Sarksyan had decided to step down due to what they described as unbearable pressure coming from the mass protests.

"Thousands of people were in the streets for days demanding his resignation and the moment came when he had no resources to suppress this movement," Ararat Mirzoyan, an opposition leader, told Reuters.

Some said Sarksyan's move was a rare example of political wisdom from a leader under pressure.

"Serzh Sarksyan has confirmed once again that he is a real statesman," said Eduard Sharmazanov, a vice speaker of parliament.

Others praised him for not resorting to a bloody crackdown to stay in power, something he had hinted at on Sunday.

Sarksyan was a close ally of Russian President Vladimir Putin and Moscow is closely watching events in Armenia, where it has two military bases. The Kremlin said on Tuesday it was pleased the situation appeared stable for now.

Many experts say it is too early to predict what lies ahead, however.

"What is needed is a sober power-sharing reconfiguration," said Richard Giragosian, a director of the Yerevan-based Regional Studies Centre.

"Yet such consensus and compromise seems very far away, and with mounting expectations and anger dangerously high, the real challenge of governance is only just beginning."