The SNP's leader at Westminster has used the last prime minister's questions before the general election to claim Theresa May is planning to cut pensions.
Angus Robertson challenged Theresa May to give a "clear and unambiguous commitment" to the triple lock system.
The prime minister responded by saying pensioner incomes would "continue to increase" under the Conservatives.
But she did not specify by how much she planned to increase them.
The triple lock, which was introduced by the coalition government in 2010, was a guarantee to increase the state pension every year by the higher of inflation, average earnings or a minimum of 2.5%.
Labour leader Jeremy Corbyn had earlier told MPs that his party would "guarantee the triple lock" if it wins the election.
Mr Robertson said Mrs May had failed to give a straight answer to his question on whether she would give a clear commitment to the policy.
He said: "I asked the prime minister a pretty simple question. It is a yes or a no, and the prime minister failed to answer."
Mr Robertson said pensioners across the country would therefore be "right to conclude that this Tory prime minister plans to ditch the triple lock on the state pension".
The SNP MP added: "Too many women already face pensions inequality, and the Tories now won't even guarantee the pensions triple lock.
"The only reason that they won't guarantee it is because they want to cut pensions".
The government has previously said it was committed to the triple lock until at least 2020 - but there has been speculation that the policy could be ditched in the Conservative manifesto ahead of the 8 June general election.
The triple lock system was criticised last year by MPs on the work and pensions committee, who said it was "unsustainable" and "unfair" on younger families and should be scrapped.
Responding to Mr Robertson, the prime minister said pensioners had benefited to the tune of £1,250 a year as a result of what the Conservatives had done to the basic state pension.
She added: "If you want to know the party in government that has improved the lot of pensioners across this country, it is the Conservative Party.
"Under a Conservative government those pensioner incomes would continue to increase.
"And it is the change in the structure of the state pension introduced by this government that is going to improve the lot of female pensioners in the future and that is going to be much better for them."
Mrs May also launched a stinging personal attack on Mr Corbyn, accusing the Labour leader of "not being up to the job" of prime minister, and said the Conservatives would offer "strong and stable leadership" for the country.
Mr Corbyn said the economy had failed under the Conservatives, with "millions of people struggling to make ends meet".
He added: "They are strong against the weak, and weak against the strong. Far from building a strong economy, schools and our NHS are being cut, people can't afford homes and millions can't make ends meet.
"That doesn't add up to a stronger economy for anyone."
He had earlier said that Labour will guarantee the triple lock, and will "treat pensioners with respect", adding: "We will not move the goalposts (for) people looking forward to retirement."
Meanwhile, Liberal Democrat leader Tim Farron criticised Mrs May's record as prime minister on a range of social and welfare issues.
He said: "She has closed the door on desperate child refugees. She has ignored the plight of those suffering under the crisis in health and social care and she is responsible for the shameful rape clause.
"Twenty years ago she berated the Conservative party for being a nasty party - but her party has never been nastier."