Anger is growing in India that the Mumbai attacks were not prevented
US Secretary of State Condoleezza Rice has called on the Pakistani government to take a "tough line" on terrorism after arriving in Islamabad for talks.
Ms Rice also said Pakistan had to mount a "robust" response to last week's attacks in the Indian city of Mumbai, which left at least 188 people dead.
India says the attackers had links to Pakistan, which Islamabad has denied.
Ms Rice arrived in Pakistan's capital after visiting India amid growing tension between the two neighbours.
In Delhi on Wednesday, she called on both countries to show moderation in their response to the Mumbai attacks.
'Robust and effective'
Speaking to reporters flying from Delhi to Islamabad with her on Thursday morning, Ms Rice said: "The global threat of extremism and terrorism has to be met by all states, taking a very tough and hard line, and so that is what I am going to discuss."
"Pakistan has to determine its own response here. It just needs to be a robust response and it needs to be effective," she added.
During her one-day visit, Ms Rice is discussing the Mumbai attacks with Pakistani President Asif Ali Zardari and Prime Minister Syed Yusuf Raza Gillani.
After holding talks with Indian government leaders on Wednesday, Ms Rice said that Pakistan had to act "fully and transparently" in efforts to bring to justice those involved in the Mumbai attacks.
"Pakistan has a special responsibility to do so," she told a news conference after meeting Indian Foreign Minister Pranab Mukherjee.
India says the attackers had links to Pakistan, which Islamabad has denied
"This is the time for everybody to co-operate and do so transparently, and this is especially a time for Pakistan to do so," she added.
Ms Rice also warned India not to take actions that would provoke "unintended consequences".
"Any response needs to be judged by its effectiveness in prevention," she said.
Last week's attacks at multiple locations in Indian's financial capital stunned the country, with many describing it as India's 9/11.
Indian authorities have said that the attackers came from Pakistan.
The Indian government has been under tremendous pressure domestically to take action against those responsible for the attack.
On Wednesday, thousands of people attended mass protests in Mumbai, blocking traffic and shouting slogans, including "Down with Pakistan" and "Shame on politicians".