Thai prime minister sees no quick end to political impasse, but willing to negotiate.
The recent protests were triggered by an amnesty bill, since abandoned by Yingluck's ruling party, which opponents feared would have cleared the way for his return.
They are the biggest and deadliest street demonstrations since 2010, when dozens of people were killed in a crackdown on mass pro-Thaksin rallies in Bangkok.
The kingdom remains tense following several days of street clashes between police and demonstrators seeking to overthrow Prime Minister Yingluck Shinawatra and curb the political influence of her brother Thaksin.
The unrest has left five people dead and more than 200 injured in Bangkok.
Demonstrators and police in Bangkok have observed a temporary truce since Wednesday for the 86th birthday of King Bhumibol Adulyadej, who is treated as a near-deity by many Thais.