Britain should cut aid spending to Pakistan and divert it to poorer countries unless "clear evidence" is produced that it is helping reduce Islamic extremism, MPs said.
A Commons committee said the UK was still giving large sums of money to a state "that has failed to adequately mobilise the substantial resources of the country to help its poor".
Nigeria was another example of a middle-income nation that benefited from significant help from British taxpayers, the cross-party international development select committee pointed out.
The proportion of the rising aid budget devoted to the poorest countries in the world - the UK recently became the first G7 member to meet a UN target of spending 0.7% of national income on development - was still too small, it concluded.
And it used its latest report to issue an explicit caution over Pakistan, which is set to benefit from £446 million of assistance in 2014/15 - making it the largest recipient of UK bilateral aid in the world.
"It is unlikely that expenditure would be so high if the country were not having to confront Islamic extremism," the committee concluded.
"If this is the case, the budget can only be justified if there is clear evidence that DfID (Department for International Development) support is effective in reducing the extremist threat.
"If not, we recommend that DfID consider reducing spending in Pakistan and increasing it in low income countries.
The committee previously said aid increases should be held back unless Pakistan's leaders impoved tax collection and paid their "fair and proportionate" share.
In their report, the MPs welcomed the UK becoming the first to meet the UN target but said spending the money effectively at a time of reductions in operating costs was a "major challenge".
Keeping costs much lower than comparable donor countries was "not in itself a virtue" if it meant staff that should be deployed in the field were stuck behind desks, it suggested.
A review of all £5 million-plus projects ordered by International Development Secretary Justine Greening might also have backfired by encouraging staff to "gold plate" them.
They should "spend less time writing the perfect business case and more in thoroughly assessing which areas to allocate funds to and in monitoring the implementation of programmes, including by spending more time in the field", the MPs said.
There was also criticism of the share of funding devoted to reacting to humanitarian disasters in relatively wealthy countries.
Britain could not afford to continue leading the world in dealing with situations such as the Syria crisis and needed to do more to persuade other high-income nations -such as France - to contribute more, committee chair, Liberal Democrat Sir Malcolm Bruce, said.
"The UK has met the target of spending 0.7% of national income on aid; others should do the same.
"UK spending on humanitarian assistance has risen substantially due partly to a very large increase in the aid budget for 2012-13. This will not, however, be repeated in future years as DfID's budget will be linked to GDP.
"It will simply not be possible for DfID to continue taking the lead in future; other countries must do more.
"DfID must not provide funds to support disasters in middle-income countries by raiding bilateral development programmes in low income countries. Rather, we argue for the percentage of income spent in low income countries to rise over time provided they are capable of absorbing it and of using aid effectively."
Staff should "spend less time in their offices and more time out in the field building local knowledge and monitoring whether UK aid money is being used effectively", he said.
A DFID spokesman said: "Our investment in overseas development, including in Pakistan, creates a safer and more prosperous world for the UK.
"Tackling poverty in the world's poorest places can mean tackling the root causes of global problems such as terrorism, which matter to us here in Britain. Education is vital to transforming Pakistan's future and is where a significant proportion of our funds are directed.
"This is firmly in the UK's own national interest."