China's president Hu Jintao was forced on the defensive today on the opening day of his state visit to the US, admitting for the first time in public that his country had to improve its human rights record.

Hu's visit, intended to improve relations between the two countries after a year of tensions over trade and diplomacy, was overshadowed by the human rights issue. It has been raised twice by Barack Obama in public, by US reporters at a press conference and by hundreds of demonstrators outside the White House.

It is the first state visit to the US by a Chinese leader in 13 years and, given China's rise in the intervening period to superpower status, there is lot riding on the outcome for both countries.

But at the joint Obama-Hu press conference, there was embarrassment for the Chinese leader when he claimed not to have heard a question from a US reporter who asked him to justify China's human rights record.

After listening to a translation of the question and of Obama's response, Hu completely ignored it. Later in the press conference, another US reporter asked him why he had not answered. Hu, laughing, claimed: "I would like to clarify. Because of the technical translation and interpretation problems, I did not hear the question about human rights."

The Chinese leader then went on to give a rare answer on human rights: "China is a developing country with a huge population, and also a developing country at a crucial stage of reform. In this context, China still faces many challenges in economic and social development. And a lot still needs to be done in China, in terms of human rights."

But he went on to remind Americans that while China is prepared to discuss human rights with the US, it would be on the basis of "mutual respect and the principle of non-interference in each other's internal affairs", basically it is a matter for China to decide.

It is unusual for a Chinese leader such as Hu to face a spontaneous press conference. Normally he restricts his remarks to scripted speeches.

China has an abysmal record on political dissent, as well as crackdowns on minorities such as Tibetans and Uighurs. Among high-profile prisoners is dissident Liu Xiaobo, the 2010 Nobel peace prize-winner.

Pro-Tibet groups and other demonstrators plan to follow Hu throughout his visit to Washington and later in the week to Chicago. Outside the White House and out of the hearing of Hu, about 200 people shouted "Killer, killer Hu Jintao".

They expected their numbers to double later for the carrying of a coffin round the White House to symbolise the death of the Chinese Communist party.

Although the US needs Chinese help in reviving its economy and with international issues such as North Korea and Iran, Obama did not shy away from the human rights issue. He raised it first at the welcoming ceremony on the White House lawn and again in a statement at the start of the press conference, at which he also called on China to engage with the Dalai Lama about Tibet.

Asked at the press conference about human rights, Obama said he had been very candid with Hu, telling him that although the countries are at different stages of development, "we have some core views as Americans about the universality of certain rights – freedom of speech, freedom of religion, freedom of assembly – that we think are very important and that transcend cultures."

Obama's raising of the issue twice in public may reflect a toughening of approach by the US towards China after what Washington sees as the failure of Beijing to respond to American overtures over the last two years.

"It is a slap in the face for Hu to raise human rights in the opening ceremony," said Nicholas Bequelin, a senior researcher with the Asia division of Human Rights Watch. He added that the Chinese side had done everything it could to avoid such embarrassment.

Elizabeth Economy, director of Asia studies at the US-based Council on Foreign Relations, said that Obama's remark would not necessarily be interpreted as a snub by Hu. "As both a winner of the Nobel peace prize and the president of the US, it was incumbent upon Obama to make such a statement, and I think he did it in a way that was clear and compelling without being insulting," she said.

Hu may view the public discussion of human rights as awkward and an embarrassment or may regard it as an opportunity at last to tackle an issue that is hurting China's global reputation. A clue will be provided by whether Chinese television and other official media report his remarks.

Hu may have liked to have got through the four-day visit without any reference to human rights and to have kept the focus instead on the pomp and ceremony associated with a state visit, the highlight of which was a state dinner scheduled at the White House for the evening.

But the visit was never going to go as smoothly as Hu would have liked. The Democratic leader in the Senate, Harry Reid, was provocative, describing Hu on as "a dictator". Reid has refused to attend the state dinner.

The new Republican house speaker, John Boehner, also declined to attend. Asked by a reporter about their absences, Hu said it was a matter for Obama.

Hu, as a sweetener to the US, came bearing gifts in the shape of $45bn (£28bn) in trade deals, almost half of which came in a promise to buy Boeing aircraft.